Prep filling - if cold, warm it in microwave. If raw, cook/steam beforehand. (You can be creative with the filling- beans, sliced protein, and reheated frozen or pre-cooked veggies are all great options)
Place 1 tortilla in the skillet and sprinkle all over with ~1/2 cup of cheese (about 1/4 of your shredded cheese pile)
Add a layer of filling over half of the tortilla.
When the cheese melts, begin lifting a corner of the tortilla and checking the underside. When you see golden-brown spots on the underside of the tortilla, the quesadilla is ready.
Transfer to the cutting board and cut into triangles (or not!).
Repeat process with the remaining tortillas