Preheat oven to 425°F. Line a baking sheet with parchment paper or lightly grease it.

In a small mixing bowl, combine all fajita seasoning ingredients: chili powder, cumin, paprika, garlic powder, onion powder, salt, pepper, and cayenne if using.

On cutting board, arrange sliced chicken, bell peppers, and onion on the prepared baking sheet in a single layer.

Drizzle olive oil over everything and sprinkle with fajita seasoning. Use tongs to toss until chicken and vegetables are evenly coated.

Spread everything out in a single layer again, making sure chicken pieces aren't overlapping for even cooking.

Roast for 20-25 minutes, stirring once halfway through with tongs, until chicken is cooked through (165°F internal temp) and vegetables are tender with some charred edges.

Remove from oven and squeeze fresh lime juice over the top if desired.

Warm tortillas: wrap in damp paper towels and microwave for 30 seconds, or heat individually in a dry skillet for 20 seconds per side.

Serve chicken and vegetables in warm tortillas with your choice of toppings: cheese, sour cream, guacamole, salsa, and cilantro. Serve with lime wedges on the side.