Heat the oven to 425°F. Combine the chili powder, cumin, smoked paprika, garlic powder, salt, and pepper in a small bowl.
Put the sliced chicken, peppers, and onion on a large rimmed sheet pan. Drizzle with the olive oil, sprinkle the seasoning over everything, and toss with your hands until evenly coated.
Spread everything into a single layer with a little space between pieces. Use two pans if the first one looks crowded.
Roast for 20 minutes, tossing once halfway through, until the chicken is cooked through (165°F) and the peppers have charred edges.
Squeeze fresh lime over the hot pan and scatter with cilantro. Serve right away with warm tortillas.