Preheat a grill to medium heat. You can also make this in a skillet on the stovetop.
For each quesadilla, brush a tortilla with olive oil. Place the tortilla on the grill or skillet and top with the desired fillings: chicken, cheese, jalapenos, bell peppers, onions or beans. Top with a second tortilla and brush the top with oil. Grill until the bottom tortilla is starting to brown, about 2 minutes. Flip and grill, covering the grill or the skillet if the cheese is not melting, until the other tortilla is beginning to brown, an additional 2 minutes.
Cut each quesadilla into quarters and garnish with cilantro, lime and sour cream if using.
For more ingredient substitution ideas, see the article below.