If you haven’t yet cooked the chicken: season breasts lightly and bake at 400°F (200°C) for 18–22 minutes or grill until internal temp reaches 165°F (74°C). Let rest, then shred with two forks.

Slice bell peppers and onion thinly so they soften quickly.

Heat 1 tablespoon olive oil in a skillet over medium-high heat. Add sliced peppers and onion, season with a pinch of salt, and sauté 4–6 minutes until softened and slightly caramelized. Transfer to a bowl.

In the same skillet, add the remaining tablespoon of oil. Add shredded chicken, sprinkle taco seasoning, and toss over medium heat just until warmed through (2–3 minutes). Season with salt and pepper.

To assemble a quesadilla: lay one tortilla flat. Evenly sprinkle a thin layer of cheese over half the tortilla (this helps seal). Top with a portion of the seasoned chicken and some sautéed peppers/onions. Add another small sprinkle of cheese, then fold the tortilla over.

Wipe the skillet clean and return to medium heat. Place the folded quesadilla seam-side down. Cook 2–3 minutes per side until golden-brown and the cheese has melted, pressing gently with a spatula.

Transfer to a cutting board and let rest 1 minute to set, then slice into wedges.

Garnish with chopped cilantro if desired and serve with sour cream, salsa, or guacamole.