Preheat the oven: Set your oven to 425°F (220°C).
Line a large sheet pan with parchment paper for easy cleanup.
Prep the chicken and veggies: Thinly slice the chicken, peppers, and onion. Keep slices roughly the same thickness for even cooking.
Make the seasoning mix: In a small bowl, combine chili powder, cumin, smoked paprika, garlic powder, onion powder, oregano, salt, and pepper.
Toss everything on the pan: Add the chicken, peppers, and onions to the sheet pan. Drizzle with olive oil and sprinkle the seasoning mix evenly.
Use your hands or tongs to coat everything well and spread into a single layer.
Roast: Bake for 18–22 minutes, stirring once halfway. The chicken should be cooked through and the veggies slightly caramelized at the edges.
Broil for char (optional): For a little char, switch the oven to broil on high for 1–2 minutes. Watch closely to prevent burning.
Finish with lime: Squeeze fresh lime over the hot fajita mix.
Taste and add a pinch more salt if needed. Sprinkle with cilantro.
Warm the tortillas: Wrap in foil and warm in the oven for 3–5 minutes, or heat briefly in a dry skillet.
Serve: Pile the chicken and veggies into tortillas. Add your favorite toppings and extra lime wedges on the side.