Combine lime juice, minced garlic, cumin, paprika, chili powder, and a pinch of salt in a bowl to create the marinade. Add sliced steak, toss to coat, and let sit for at least 15 minutes to tenderize and infuse flavor.
While the steak marinates, heat a tablespoon of oil in a large skillet over high heat until shimmering and just starting to smoke.
Add the marinated steak slices to the hot skillet in a single layer. Sear quickly for about 1-2 minutes per side until nicely browned and just cooked through. Remove from the skillet and set aside.
Add another tablespoon of oil to the same skillet. Toss in sliced peppers and onions, spreading them out evenly.
Cook the vegetables over high heat, stirring occasionally, until they are caramelized and slightly charred around the edges, about 5-7 minutes. The peppers should be tender and the onions sweet and golden.
Return the cooked steak to the skillet with the vegetables. Toss everything together and cook for another 1-2 minutes until heated through and slightly caramelized.
Warm the tortillas in a damp towel in the microwave for about 30 seconds until soft and pliable.
Serve the sizzling steak and vegetable mixture with warm tortillas, allowing everyone to fill and fold their fajitas as desired.
