In a small bowl, combine chili powder, cumin, paprika, sugar, garlic powder, onion powder, cayenne pepper, and salt.
In a plastic bag, add 2 pounds chicken, ¼ cup minced cilantro, 3 tablespoons lime juice, and 2 tablespoons of fajita seasoning. Mash until evenly coated. Marinate at least 30 minutes (room temperature) or up to 1 hour (refrigerated).
In a large skillet over medium-high heat, heat 2 tablespoons olive oil until shimmering. Add chicken and cook until browned and cooked through, 160 degrees. Transfer chicken to a cutting board and rest. Do not discard fat in skillet.
Meanwhile, to the skillet with the fat over medium-high heat, add sliced bell peppers and red onion, and cook until tender, about 5 minutes.
Push peppers and onions to one side and add chicken back to skillet for serving.
Serve with tortillas, cheese, salsa, and sour cream.
