Preheat your oven to 425°F (220°C).

Slice the flank steak or sirloin thinly against the grain and chop bell peppers and red onion into strips.

In a small bowl, combine chili powder, smoked paprika, ground cumin, garlic powder, onion powder, dried oregano, salt, and pepper.

In a large mixing bowl, add the sliced steak, chopped peppers, onions, olive oil, and spice blend, then toss until evenly coated.

Spread the seasoned steak and vegetables in a single layer on a large rimmed baking sheet.

Roast in the oven for approximately 15-20 minutes until the vegetables are charred and the steak is cooked through.

Warm tortillas in a clean kitchen towel or dry skillet over low heat for about 30 seconds on each side.

Serve the fajita mixture hot in warm tortillas with toppings like lime wedges, cilantro, sour cream, guacamole, and salsa.