Slice steak against the grain into 1/4-inch strips. Toss with lime juice, oil, garlic, chili powder, cumin, and salt. Let sit 10 minutes.

Heat a cast iron skillet over high heat. In batches, sear steak strips 2 minutes per side until charred and just cooked through.

Warm tortillas in a dry skillet until pliable.

Stack two tortillas, add steak, top with onion, cilantro, and a squeeze of lime. Serve immediately.