1.Cut each chicken breast lengthwise in 3 strips; cut crosswise into thin pieces.
2.Combine with the fajita seasoning and mix well.
3.Heat the oil in a large skillet over medium heat.
4.Add the chicken and cook 7 to 8 minutes or until no longer pink in the center, stirring frequently.
5.Stir in the bell peppers and onion. Cook the vegetables for 5 to 7 minutes or until the vegetables are tender.
6.For each quesadilla, sprinkle ¼ cup Cheddar cheese on half of a tortilla. Spoon about ½ cup of the chicken mixture over the cheese. Top with ¼ cup Monterey Jack cheese and fold the tortilla over, forming a half moon. Press lightly.
7.Spray a skillet or griddle with cooking spray; warm to medium heat.
8.Lightly brown each quesadilla for 2 to 3 minutes per side until the cheese is melted.
9.Cut each into 4 wedges and serve with sour cream.