Prepare Ingredients: Gather all ingredients and preheat the broiler. Lightly grease a baking sheet.
Broil Chicken: Toss chicken with fajita seasoning, then spread onto the prepared baking sheet. Place under the broiler and cook until chicken is cooked through, about 5 minutes.
Preheat Oven: While the chicken is cooking, preheat the oven to 350°F (175°C).
Cook Vegetables: Heat oil in a large saucepan over medium heat. Stir in bell peppers, onion, and broiled chicken. Cook and stir until vegetables have softened, about 10 minutes.
Assemble Quesadillas: Layer half of each tortilla with the chicken and vegetable mixture, Cheddar cheese, Monterey Jack cheese, and bacon bits. Fold tortillas in half.
Bake Quesadillas: Place the assembled quesadillas onto a baking sheet and bake in the preheated oven until the cheeses have melted, about 10 minutes.
Serve: Remove from the oven and cut each quesadilla into wedges. Serve with sides of salsa and sour cream. Enjoy your delicious chicken and vegetable quesadillas!