Stack tortillas and wrap tightly in foil. Heat in 350 degree F oven for 10 minutes to soften.
Meanwhile, for filling, in a skillet cook onion in hot oil until tender; add refried beans. Cook and stir until heated through. Spoon about 1/4 cup of the filling onto each tortilla just below center and to within 1-inch of the edge. Divide cheese among tortillas. Fold bottom edge of each tortilla up and over filling. Fold opposite sides in over filling . Roll up from the bottom. Place on a baking sheet. Bake in a 350 degree F oven about 10 minutes or until heated through. Serve with lettuce and salsa.