In a small bowl, whisk together lime juice, olive oil, minced garlic, cumin, chili powder, smoked paprika, oregano, salt, and pepper.
Place steak pieces in a zip-top bag or shallow dish. Pour marinade over, turning to coat. Seal and refrigerate for at least 30 minutes, up to 4 hours.
Slice bell peppers and onion into thin strips, about 1/4 inch wide. Toss with a splash of oil and a pinch of salt.
Heat a large cast-iron skillet or grill pan over high heat until smoking. Remove steak from marinade, letting excess drip off. Cook for 3-4 minutes per side until internal temperature reaches 145°F (63°C) for medium-rare (or to desired doneness). Transfer to a cutting board and tent with foil. Let rest 5 minutes.
In the same skillet over high heat, add a drizzle of oil and the peppers and onions. Spread in a single layer and cook without stirring for 2 minutes. Then toss and cook another 2-3 minutes until lightly charred but still crisp-tender.
While steak rests, warm tortillas in a dry skillet over medium-high heat, 15-20 seconds per side until pliable and slightly puffed. Keep wrapped in a towel. Slice the rested steak against the grain into thin strips. Pile the meat and vegetables back into the hot skillet to sizzle. Serve immediately with warm tortillas, lime wedges, and toppings.