1. If your chicken is raw, cut it in cubes and cook in a little bit of olive oil, until no longer pink in the center (about 8 minutes). I used leftover roasted chicken.
2. In a skillet, heat olive oil. Add onion, peppers and fajita seasoning, cook until the vegetables are tender (about 7 minutes).
3. Warm a large skillet with butter over low-medium heat. Place tortilla, sprinkle 1/4 cup of Cheddar cheese on half of it.
4. Spoon about 1/2 cup of the chicken over the cheese. Top with the peppers and onion mixture, then sprinkle the other half of the tortilla with Monterey Jack cheese.
5. Fold the tortilla over, pressing lightly. When the bottom is lightly browned, flip over and lightly brown the other side.
6. Repeat the process with the remaining tortillas.
7. Cut into wedges if desired. Serve with sour cream.