Preheat and prep: Heat your oven to 425°F (220°C).
Line a large sheet pan with parchment for easy cleanup. Slice the chicken, peppers, and onion into thin strips so everything cooks evenly.
Make the fajita seasoning: In a small bowl, combine chili powder, cumin, smoked paprika, garlic powder, onion powder, oregano, cayenne (if using), salt, and black pepper.
Dump-and-go setup: Add the chicken, peppers, and onion to the sheet pan. Drizzle with olive oil and sprinkle the seasoning mix over everything.
Toss directly on the pan to coat well. Spread into an even layer.
Roast: Bake for 18–22 minutes, tossing once halfway through, until the chicken is cooked through and the peppers are tender with a little char on the edges.
Finish with lime: Zest and juice the lime over the hot fajitas and toss. Taste and adjust salt or heat as needed.
Warm the tortillas: Wrap tortillas in foil and warm in the oven for the last 5 minutes, or heat them in a dry skillet until pliable.
Serve: Pile the chicken and peppers into warm tortillas.
Add your favorite toppings and dig in.