Set your oven to 400°F to preheat.
Combine chili powder, paprika, onion powder, garlic powder, cumin, cayenne pepper, sugar, and salt in a small bowl to create the fajita seasoning.
Slice the onions and bell peppers into thin strips about 1/4 inch wide, and also cut the chicken breast into thin strips.
Place the chicken and sliced vegetables onto a large baking sheet or casserole dish.
Pour the cooking oil evenly over the chicken and veggies, then sprinkle the homemade fajita seasoning on top.
Carefully toss everything with your hands until all pieces are coated well with oil and seasoning, then spread them out evenly on the pan.
Bake in the preheated oven for 35 to 40 minutes, stirring the mixture once halfway through cooking.
Once done, squeeze the juice from half of the lime over the cooked chicken and vegetables.
To serve, spoon some of the chicken and pepper mixture into each tortilla and garnish with cilantro, a dollop of sour cream, and an extra squeeze of lime if you like.
