Season the chicken strips with 1 tablespoon of the fajita seasoning.

Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add the chicken and cook for 5-10 minutes, stirring occasionally, until fully cooked, no longer pink, and slightly charred. Remove the chicken from the skillet and set aside. Wipe the skillet clean.

Add the remaining 1 tablespoon of olive oil to the skillet and heat. Add the onions and sauté for 2 minutes until slightly translucent. Add the bell peppers and the remaining 1 tablespoon of fajita seasoning. Mix well and cook for 2-3 minutes until the peppers are slightly tender. Return the chicken to the skillet, mix with the vegetables, and cook for 1 additional minute.

Heat a clean skillet over medium heat and melt a bit of butter. Place a tortilla in the skillet and swirl it around to coat with butter. Add a portion of the chicken and vegetable mixture on one half of the tortilla, then sprinkle about ¼ cup of cheese on top. Fold the tortilla over to create a half-moon shape, or place another tortilla on top for a full-circle quesadilla.

Cook the quesadilla for 1-2 minutes on one side until golden and crispy, then carefully flip it over and cook the other side until golden and the cheese is melted. Remove from the skillet and cut into quarters.

Repeat the process with the remaining tortillas and filling.

Serve the quesadillas hot with salsa and sour cream on the side.