Preheat the oven to 400 degrees. Mix all of the spices for the fajita seasoning in a small bowl and set aside.

Cut the onion and bell peppers into 1/4-inch wide strips. Place them in a large 13×15-inch casserole dish or a large baking sheet. Slice the chicken breast into very thin strips and add it to the casserole dish with the vegetables.

Drizzle the vegetable oil over the chicken and vegetables, then sprinkle the fajita seasoning mix over top. Toss the ingredients until everything is well coated in oil and seasoning. Bake in the preheated oven for 35-40 minutes, stirring once half way through. Squeeze the juice from the lime over top of the meat and vegetables after they come out of the oven.

Scoop a small amount of meat and vegetables into the center of each tortilla. Top with a few sprigs of cilantro, a dollop of sour cream, and an extra squeeze of lime if desired.