Boil red potatoes to 90 percent cooked and cool in the refrigerator until cold. When potatoes are cold, cut into medium sized chunks and saute in 1 tablespoon of margarine and 1 tablespoon of butter. When the potatoes are almost finished sauteing, begin to cook the bacon crisply and cut into small pieces. Set aside. Just before the potatoes are browned, sprinkle garlic, onions, salt and pepper onto the potatoes. Drain off excess oil. Set aside. Saute mushrooms. Set aside. Whip 3 eggs together. Grease a 10-inch omelet pan with margarine over a medium heat. Have all other ingredients ready to assemble quickly after the eggs are cooked. Put the eggs in a pan and cook slowly over a medium heat. With a spatula, push the eggs to the center of the pan. Remember that this is an open omelet so do not fold over. As the eggs begin to seal on the bottom, keep folding the loose eggs under the cooked portion. When almost all the loose egg is cooked, clip the eggs over. Lay the cooked eggs flat on a plate. Spread sour cream, and then place potatoes on the eggs, followed with mushrooms, tomatoes and bacon. Top with feta cheese.