01 - Combine shredded chicken and BBQ sauce in a mixing bowl, ensuring all pieces are thoroughly coated.
02 - Place tortillas on a flat surface and evenly spread BBQ chicken, sliced onion, bell pepper, corn, Monterey Jack cheese, cheddar cheese, and cilantro (if desired) over half of each tortilla.
03 - Fold each tortilla over to create a half-moon shape, pressing gently to seal the edges.
04 - Warm a large skillet or griddle over medium heat and lightly brush with olive oil or butter.
05 - Working in batches, cook each quesadilla for 2 to 3 minutes per side until golden brown and the cheese is fully melted.
06 - Transfer cooked quesadillas to a cutting board, allow to rest for 1 minute, then slice into wedges and serve immediately.