In a large bowl, combine the shredded chicken, cheddar cheese, Monterey Jack cheese, red onion, and bell pepper.
Place a flour tortilla on a flat surface and sprinkle 0.5 cup of the chicken mixture onto one half of the tortilla.
Fold the tortilla in half, covering the chicken mixture.
Heat a large skillet over medium heat. Place the quesadilla in the skillet and cook for 3-4 minutes per side, or until golden brown and the cheese is melted.
Remove the quesadilla from the skillet and let it cool slightly before slicing into wedges. Serve immediately.
Notes
Serve with sour cream, salsa, or guacamole for dipping.