In a bowl, combine the shredded chicken, diced bell pepper, diced onion, and taco seasoning. Mix until well combined.
Heat 1 tablespoon of olive oil in a skillet over medium heat.
Place one tortilla in the skillet. Sprinkle half of the cheddar and Monterey Jack cheese on one half of the tortilla.
Layer half of the chicken mixture over the cheese, then top with more cheese.
Fold the tortilla in half to cover the filling and press gently to seal.
Cook for about 3-4 minutes, or until the bottom is golden brown and the cheese starts to melt. Flip the quesadilla carefully with a spatula and cook for another 3-4 minutes on the other side.
Remove the quesadilla from the skillet and repeat the process for the remaining tortillas and filling.
Cut each quesadilla into wedges and serve warm with salsa and sour cream if desired.
Ensure the cooked chicken is well-seasoned for the best flavor.
Store any leftover quesadillas in an airtight container in the refrigerator for up to 2 days. Reheat in a skillet before serving.