01 - In a mixing bowl, whisk together olive oil, smoked paprika, chili powder, cumin, garlic powder, cayenne pepper, salt, and black pepper. Coat the chicken breasts thoroughly with the spice marinade.
02 - Preheat a grill or grill pan to medium-high heat. Place chicken breasts on the grill and cook for 5 to 6 minutes per side, or until the internal temperature reaches 165°F and juices run clear. Transfer to a plate and let rest for 5 minutes before slicing thinly or dicing.
03 - While chicken is grilling, shred Monterey Jack and cheddar cheeses. Thinly slice bell pepper and red onion. Slice pickled jalapeños and chop fresh cilantro.
04 - Lay one flour tortilla flat on a cutting board. On half of the tortilla, arrange a mixture of Monterey Jack and cheddar cheese, followed by sliced grilled chicken, bell pepper, red onion, pickled jalapeños, and cilantro. Fold tortilla in half to cover the filling.
05 - Heat butter or neutral oil in a large skillet over medium heat. Carefully add the filled tortilla and cook for 2 to 3 minutes per side, pressing gently with a spatula, until golden brown and cheese is melted. Repeat with remaining tortillas and filling.
06 - Using a sharp knife or pizza cutter, cut each grilled quesadilla into wedges. Serve immediately, accompanied by salsa, guacamole, or sour cream as desired.