Step 1

Cut 1 1/2 pounds flank steak across the grain into rough 3x1/2 inch strips and place in a medium bowl. Add 1 1/2 teaspoons ground cumin, 1 teaspoon kosher salt, and 1 teaspoon ground black pepper, and toss to coat. Let sit at room temperature for 10 minutes.

Step 2

Meanwhile, prepare the following: Halve and cut 1 large red onion into 1/2-inch thick slices. Stem 1 fresh or frozen ají amarillo chili pepper and slice crosswise into thin rounds. Mince 2 garlic cloves. Core and cut 2 medium plum tomatoes into 8 wedges. Finely chop the leaves and tender stems from 1/4 bunch fresh cilantro until you have 1 tablespoon.

Step 3

Heat 2 tablespoons of the neutral oil in a wok or 12-inch cast-iron skillet over high heat until smoking. Add half the beef and spread into a single layer. Cook until browned, about 30 seconds per side. Transfer to a plate. Repeat cooking the remaining beef and adding to the plate.

Step 4

Add the remaining 1 tablespoon neutral oil to the pan. Add the onion and cook just until crisp-tender, about 1 minute. Transfer to the plate with the beef.

Step 5

Add tomatoes to the pan and sear one side until blistered, about 30 seconds. Add the garlic and ají amarillo and cook until fragrant, about 30 seconds. Add 1/4 cup red wine vinegar and 3 tablespoons soy sauce, scraping up the browned bits from the bottom of the pan with a wooden spoon. Return the beef, onion, and the accumulated juices on the plate to the pan and cook until the sauce thickens slightly, about 1 minute.

Step 6

Divide 2 cups cooked long-grain white rice and 2 cups French fries between 4 plates. Spoon the lomo saltado onto the plates with the pan juices, then garnish with the cilantro.