01 - Whisk together olive oil, lime juice, garlic, smoked paprika, cumin, chili powder, oregano, salt, and pepper in a large bowl. Add the flank steak and toss to coat thoroughly. Cover and refrigerate for at least 20 minutes, or up to 2 hours for deeper flavor penetration.
02 - Preheat a grill or grill pan over high heat until smoking hot. Remove steak from marinade and allow excess to drip off.
03 - Grill the flank steak for 4–5 minutes per side for medium-rare doneness, adjusting time to reach your preferred internal temperature. Transfer to a cutting board, tent loosely with foil, and rest for 5 minutes to allow juices to redistribute.
04 - While steak rests, heat 1 tablespoon olive oil in a large skillet over medium-high heat. Add sliced peppers and onions, season with salt and pepper, and sauté until tender-crisp and slightly charred, approximately 6–8 minutes.
05 - Heat tortillas directly on the grill or in a dry skillet for 30 seconds per side until warm and pliable.
06 - Slice the rested steak thinly against the grain at a 45-degree angle to ensure tenderness.
07 - Arrange grilled steak slices on a large platter with sautéed peppers and onions. Serve alongside warmed tortillas, avocado slices, sour cream, fresh salsa, chopped cilantro, and lime wedges for diners to build their own fajitas.