In a large nonstick skillet, heat 1 tablespoon of vegetable oil over medium heat.
Add chicken, bell peppers, onion, chili powder, salt, cumin, garlic powder, and pepper to the skillet. Cook for 5-7 minutes, stirring occasionally, until peppers and onions are soft.
Transfer the cooked mixture to a bowl and wipe out the skillet with a paper towel.
Return the skillet to medium heat and add about 1 teaspoon of the remaining oil.
Place a tortilla in the skillet. Sprinkle 1/3 cup cheese on half the tortilla.
Add 1/3 cup of the chicken mixture on top of the cheese.
Fold the tortilla in half over the filling.
Cook until the bottom is golden, about 2-3 minutes.
Flip and cook the other side until golden and cheese is melted, about 2 minutes more.
Repeat with remaining tortillas and filling, adding a little oil to the pan for each quesadilla as needed.
Cut each quesadilla in half and serve with sour cream and salsa if desired.
Notes
PRO TIP: For extra flavor, squeeze a little lime juice over the chicken fajita mixture before folding the quesadillas. It adds a zesty kick!