3 egg white omelet cheddar filling Recipes

eggs, unsalted butter , plus melted butter for brushing finished omelet, very finely grated gruyere cheddar , monterey jack, or other cheese of your choice, salt, pepper, variation --with sauteed mushroom and thyme filling, unsalted butter, shallot , minced (about 1 tbsp), white mushrooms (about 2 oz), cleaned and cut into slices 1/4 inch thick, minced fresh thyme leaves, variation -- with sauteed red bell pepper filling wih mushroom and onion, unsalted butter, onion , chopped fine, white mushroom (about 1 oz), cleaned and sliced 1/4 inch thick, red bell pepper (about 2 oz), seeds discarded, cut into 1/2-inch dice, minced fresh parsley leaves

egg whites, water, dill, chopped (optional), spinach, loosely packed and thinly sliced, salt, black pepper, ground, tomato, finely chopped, fat-free cheddar cheese