Combine chili powder, cumin, smoked paprika, garlic powder, oregano, salt, and pepper in a small bowl.
Toss chicken with 1 tbsp oil, half the spice blend, and 1 tbsp lime juice. Let stand 10 minutes.
Heat a large skillet over medium-high. Add 1 tbsp oil. Cook peppers and onion until tender and lightly charred, 5–7 minutes. Transfer to a plate.
Add chicken to the hot skillet in an even layer. Sear without stirring 2 minutes, then cook, stirring, until just cooked through, 3–4 minutes.
Return peppers and onion to the pan. Sprinkle in remaining spice blend and the last 1 tbsp lime juice. Toss 1 minute to coat.
Warm tortillas in a dry skillet or microwave until pliable.
Fill warm tortillas with chicken and veggies. Finish with cilantro, salsa, sour cream, and cheese.