Place oven rack in lowest rack position; heat oven to 400°F. Spray 1 side of each tortilla with cooking spray. On each of 2 large ungreased cookie sheets, place 2 tortillas sprayed sides down. Spread 1/4 cup refried beans on each. Top each with onions, tomato and cheese.
Bake 1 cookie sheet at a time on lowest oven rack 10 to 12 minutes or until bottoms are golden brown and cheese is melted and bubbly. Cut into wedges to serve.