01 - Whisk together olive oil, lime juice, garlic, smoked paprika, cumin, chili powder, oregano, salt, and pepper in a large bowl. Add flank steak and toss to coat thoroughly. Cover and refrigerate for at least 20 minutes, up to 2 hours for deeper flavor penetration.
02 - Heat grill or grill pan over high heat until properly preheated. Remove steak from marinade and allow excess to drip off.
03 - Place steak on preheated grill and cook for 4–5 minutes per side for medium-rare doneness, adjusting time to reach preferred internal temperature. Transfer to cutting board, tent loosely with foil, and rest for 5 minutes.
04 - While steak rests, heat 1 tablespoon olive oil in large skillet over medium-high heat. Add sliced peppers and onions, season with salt and pepper, and sauté until tender-crisp with slight charring, approximately 6–8 minutes.
05 - Heat tortillas on grill or in dry skillet for 30 seconds per side until pliable and warm.
06 - Cut rested steak thinly across the grain for optimal tenderness.
07 - Arrange grilled steak slices with sautéed peppers and onions on large serving platter. Accompany with warmed tortillas, avocado slices, sour cream, fresh salsa, cilantro, and lime wedges for diners to build their own fajitas.