Peru’s lomo saltado is fusion cooking at its easiest and most approachable, a quick stir-fry of soy-marinated beef, tomatoes and hot peppers. It’s part of the chifa cuisine—Asian-influenced dishes brought to the South American country by indentured Chinese workers in the late 19th century. For our take, we developed flavor by mixing ground cumin into the soy sauce marinade. Tenderloin is often used, but we preferred sirloin tips (also called flap meat) for their meatier flavor as well as lower price. And we seared the meat instead of stir-frying. Readily available jalapeño peppers made a good substitute for the traditional yellow aji peppers. If you prefer little to no spiciness, halve and seed the jalapeño before slicing it into half rings. Classic lomo saltado is frequently served over french fries; your favorite, frozen or otherwise, would be a good choice here. Steamed rice is an equally good, and lighter, accompaniment.
Don’t cook the beef without patting it dry. Marinating in soy sauce adds flavor, but also moisture. Drying the beef helps ensure that the slices sear nicely, rather than steam. Also, cook it in two batches; crowding the pan inhibits browning.
In a medium bowl, combine the steak, cumin, 1 teaspoon each salt and pepper, and 2 tablespoons of the soy sauce. Marinate at room temperature for 10 minutes. Drain, pat the meat dry and transfer to a plate.
In a 12-inch skillet over high, heat 1 tablespoon of the oil until barely smoking. Add half of the meat in a single layer and cook, turning once, until well browned on both sides, 2 to 3 minutes total. Transfer to a plate. Repeat with 1 tablespoon of the remaining oil and the remaining meat.
In the same pan over medium-high, heat the remaining 1 tablespoon oil until shimmering. Add the onion and cook until just starting to soften, stirring, for
2 minutes. Stir in the vinegar and remaining 3 tablespoons soy sauce, scraping the bottom of the pan.
Cook for 1 minute, or until the sauce thickens slightly. Stir in the garlic and jalapeño and cook until the garlic is fragrant, about 30 seconds. Add the tomatoes, the meat and any accumulated juices. Cook until the meat is just warmed through, 30 seconds. Taste and season with salt and pepper.