Whisk egg whites until light and frothy; set aside. Heat an omelet pan to temperature over medium heat. Melt butter and saute onions, garlic and cumin together. When onions become translucent, add mushrooms. Stir until wilted. Add spinach and mushrooms. Season with salt and crushed red peppercorns. Pour in egg whites. Let the eggs cook undisturbed until the edges of egg whites start to cook through and turn solid white. Gently lift the edges of the egg whites and tilt the pan so the uncooked egg runs under the cooked part and cooks for another minute. Fold egg white omelet and cook until eggs have puffed and are done. Serve immediately by itself or with garlic potatoes. Makes 1 serving.