1. Lightly brush one side of each tortilla with cooking oil or lightly coat with cooking spray. Divide cheese evenly among un-oiled sides of 2 larger or 3 smaller tortillas. Add pepper slices, chopped tomato, and cilantro. Top with remaining tortillas, oiled sides up.
2. Heat a heavy skillet or griddle over medium heat. Cook quesadillas, one at a time, about 1 to 2 minutes per side, or until cheese melts and tortillas are lightly browned. Cut each quesadilla into 4 wedges. Serve warm with sour cream.