01 - In a mixing bowl, combine the shredded chicken with the BBQ sauce and toss until thoroughly coated.
02 - Lay out the flour tortillas on a clean, flat surface. Evenly distribute the marinated chicken, sliced red onion, bell pepper, corn kernels, Monterey Jack cheese, and cheddar cheese over one half of each tortilla. Sprinkle with chopped cilantro, if using.
03 - Carefully fold the plain half of each tortilla over the filled half, creating a semi-circular shape. Gently press to seal the edges.
04 - Heat a large skillet or griddle over medium heat. Lightly brush the cooking surface with olive oil or butter.
05 - Place the assembled quesadillas onto the heated skillet or griddle. Cook for 2-3 minutes per side, or until the tortillas are golden brown and the cheese is completely melted and gooey.
06 - Remove the cooked quesadillas from the skillet. Allow them to cool slightly for about 1 minute, then slice each quesadilla into wedges. Serve immediately while warm.