In a mixing bowl, whisk together lime juice, minced garlic, cumin, salt, and pepper to create the marinade.

Place the flank steak on a cutting board and pound with a meat mallet or rolling pin to about 1/2-inch thickness.

Submerge the steak in the marinade and let it sit for at least 30 minutes at room temperature or up to 8 hours in the refrigerator.

Heat the olive oil in a large skillet over medium-high heat (about 375°F) until shimmering.

Remove the steak from the marinade, allowing excess to drip off, and place in the hot skillet.

Sear the steak for 4 to 5 minutes on each side until deeply browned and cooked through.

Transfer the steak to a cutting board and let it rest for 10 minutes to allow juices to redistribute.

Use a sharp knife to slice the steak thinly against the grain into strips.

Add the sliced steak back to the skillet and cook for an additional 2 to 3 minutes, pressing pieces to crisp the edges.

In the same skillet, add the sliced onion and sauté for 5 to 7 minutes until caramelized.

Serve the steak topped with sautéed onions and garnish with chopped fresh cilantro and lime wedges.