Preheat the oven. Set it to 425°F (220°C).
Line a large sheet pan with parchment for easy cleanup, or use a well-seasoned pan.
Slice the chicken and veggies. Cut the chicken into thin strips, about 1/2 inch wide. Slice peppers and onion into similar-sized strips for even cooking.
Make the seasoning. In a small bowl, mix olive oil, lime zest and juice, minced garlic, chili powder, cumin, paprika, oregano, salt, black pepper, and cayenne if using.
Toss everything on the pan. Add chicken, peppers, and onions to the sheet pan. Pour the seasoning over and toss with tongs or your hands until everything is well coated.
Spread into an even layer without crowding.
Roast. Bake for 15 minutes. Remove the pan, toss the mixture, then return to the oven for 7–10 more minutes, until the chicken is cooked through and the peppers are tender with lightly charred edges. Target internal temperature: 165°F (74°C).
Broil for char (optional). For extra color, switch to broil on high for 1–2 minutes. Watch closely to avoid burning.
Finish with freshness. Sprinkle with chopped cilantro and an extra squeeze of lime.
Taste and adjust salt if needed.
Warm the tortillas. Wrap in foil and place in the oven for the last 5 minutes, or heat in a dry skillet until pliable.
Serve. Pile the chicken and veggies into warm tortillas. Add your favorite toppings. For a lighter option, serve over romaine or cauliflower rice.