Coat a large nonstick skillet with cooking spray, place over medium-high heat until hot. Add onion, saute 12 minutes or until very tender, adding water, 1 tablespoon at the time, to prevent scorching. Season with salt and black pepper to taste.
Remove onion from pan, keep warm.
Cook meatless burgers in pan according to package directions.
Divide cooked onion evenly over 4 slices of bread and top each with 1 burger patty and 1 cheese slice. Cover with remaining 4 slices of bread.
Place pan over medium heat until hot. Coat one side of each bread slices with cooking spray and place 2 sandwiches, coated side down, in pan, and cook about 3 minutes or until brown.
Coat top sides of sandwiches with cooking spray, turn sandwiches over, and cook for about 3 minutes or until brown.
Repeat procedure with remaining sandwiches.
If you own a indoor grill (such as George Forman) you can also make them, once assembled, on the grill and you dont' have to turn them over. Enjoy.