Lomo Saltado Mushroom Burgers with Fries Inside
Seared oyster mushrooms stand in for beef in this Peruvian-inspired burger. They are tossed over high heat with red onion, tomato, soy sauce and vinegar, then piled onto a toasted bun with crisp fries and a creamy ají mayo. It tastes like lomo saltado, and you can eat it in your hands.
Steps
Before you start
- Start the fries first. They bake while you prep and cook, so everything finishes together.
- Tear the mushrooms by hand into thick strips. Don't wash them under running water. Wipe off any dirt with a damp paper towel, because wet mushrooms steam instead of sear.
- Have every ingredient cut and measured before you turn on the stove. The stir-fry moves fast, and the mushrooms need high heat.
- Use a 12-inch (30 cm) skillet or wide wok. A smaller pan crowds the mushrooms and they won't brown.
Bake the friesOven 425°F / 220°C
- Position an oven rack in the center and heat the oven to 425°F (220°C).
- Spread the frozen fries in a single layer on a large rimmed baking sheet, leaving a little space between them.
- Bake for 22–25 minutes, flipping them once halfway, until deep golden and crisp at the edges.
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Ready when: Deep golden brown and crisp at the edges
Tip: Don't pile the fries on top of each other or they will steam and turn soft.
Prep and mix sauce
- While the fries bake, trim and tear the mushrooms, cut the onion and tomatoes, mince the garlic, and chop the cilantro.
- In a small bowl, stir together the mayonnaise, ají amarillo paste and lime juice until smooth and evenly orange-yellow.
- In another small bowl or cup, combine the soy sauce, vinegar, cumin and pepper.
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Ready when: Sauce is smooth with no streaks of paste
Tip: Keep the tomato wedges thick. Thin slices break down into mush in the hot pan.
Toast the buns
- Heat a dry skillet or griddle over medium heat for 1 minute.
- Toast the buns cut-side down for 1–2 minutes, until golden and slightly crisp.
- Set them aside, cut-side up.
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Ready when: Cut sides are golden and feel dry and crisp
Tip: A well-toasted bun makes a barrier that keeps the juicy filling from soaking through.
Sear first mushroom batch
- Heat the 12-inch skillet or wok over high heat for 2 minutes until very hot.
- Add 1 tablespoon (15 ml) of the oil, then half the mushrooms in a single layer.
- Leave them untouched for 2 minutes, then toss and cook another 2–3 minutes.
- Transfer to a plate.
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Ready when: Edges are deep golden brown and the liquid they released has evaporated
Tip: Don't salt the mushrooms yet. Salt draws out water and prevents browning.
Sear second batch
- Wipe out any dark bits if needed.
- Add another 1 tablespoon (15 ml) oil to the same pan over high heat, then cook the remaining mushrooms the same way for 4–5 minutes.
- Add them to the plate.
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Ready when: Browned and slightly crisp at the edges, reduced to about half their original volume
Cook onion and garlic
- Add the remaining 1 tablespoon (15 ml) oil to the pan, still over high heat.
- Add the onion wedges and stir-fry for 2 minutes until they are charred in spots but still crunchy.
- Add the garlic and stir for 30 seconds until fragrant.
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Ready when: Onion edges are lightly charred but the centers still have bite; garlic smells fragrant, not burnt
Tip: If the garlic begins to darken, take the pan off the heat right away.
Toss the lomo saltado
- Add the tomato wedges and return the mushrooms to the pan.
- Pour the soy sauce mixture over everything and toss for 1–2 minutes, until the tomatoes just start to soften and the sauce reduces to a glaze that coats the mushrooms.
- Remove from the heat, stir in the cilantro, and taste.
- Add up to ¼ teaspoon salt if needed.
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Ready when: Tomatoes are softened but still hold their shape, and only a thin, glossy sauce remains in the pan
Tip: Serve right away. Leftover stir-fry will make the bun soggy.
Salt the fries
- Remove the fries from the oven and sprinkle with ¼ teaspoon salt right away, tossing on the pan so they are evenly coated.
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Ready when: Fries are crisp and evenly seasoned
Tip: Salt sticks best while the fries are still hot.
Assemble and serve
- Spread about 1 tablespoon of ají mayo on each bun half.
- Pile one quarter of the mushroom mixture onto each bottom bun, spooning over a little of the pan sauce.
- Top with a generous handful of fries, then close with the top buns.
- Serve straight away with the remaining fries and mayo on the side.
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Ready when: Burgers are tall and stacked, with the filling sitting neatly on the bun
Tip: Eat these within a few minutes while the fries are still crisp.
Good to know
Tips
- High heat and a roomy pan are what give the mushrooms their seared, meaty edges. Cook in two batches rather than one crowded pile.
- Keep the onion and tomato slightly crunchy and firm. Their fresh texture is a hallmark of lomo saltado.
- Add the soy sauce and vinegar last. Adding them early boils the mushrooms and makes the dish watery.
- For extra heat, add a thinly sliced fresh chile with the onion.
Make ahead
You can mix the ají mayo up to 3 days ahead and refrigerate it. Prep the vegetables and tear the mushrooms up to 1 day ahead and store them in separate airtight containers in the fridge. Bake the fries and cook the mushrooms just before serving.
Storage & reheating
Store leftover mushroom filling, fries and mayo separately in airtight containers in the fridge for up to 3 days. Do not store assembled burgers. Reheat the filling in a hot skillet for 2–3 minutes, and re-crisp the fries on a baking sheet at 425°F (220°C) for 5–8 minutes. The cooked filling can be frozen for up to 2 months, but the mushrooms soften. Thaw in the fridge overnight before reheating. Leave room-temperature storage to under 2 hours.
Substitutions
- oyster mushrooms → King oyster mushrooms or cremini mushrooms. Slice king oysters ½ inch (1.25 cm) thick. Cremini should be thickly sliced and may need an extra minute to brown.
- ají amarillo paste → 1 tsp sriracha plus ½ tsp ground turmeric. This gives similar heat and color but not the fruity flavor of ají amarillo.
- mayonnaise (vegan if needed) → Plant-based mayonnaise or Greek yogurt. Use vegan mayo to keep the burger fully vegan. Greek yogurt gives a tangier sauce.
- soy sauce → Tamari or coconut aminos. Tamari keeps it gluten-free if you also choose gluten-free buns and fries. Coconut aminos is sweeter, so use 4 tbsp (60 ml).