1. Place potato in a small saucepan; cover with water. Bring to a boil, and cook 10 minutes or until tender; drain.
2. Preheat oven to 450°.
3. Combine 1/4 cup cheese, egg whites, and egg yolk in a bowl; stir well, and set aside. Melt margarine in a 10-inch nonstick skillet over medium heat. Add potato, onion, bell pepper, Canadian bacon, and garlic; saute 5 minutes. Stir in egg mixture; spread evenly in bottom of skillet. Reduce heat to medium-low, and cook 5 minutes or until almost set.
4. Wrap handle of skillet with foil; place skillet in oven, and bake at 450° for 5 minutes or until set. Sprinkle with remaining 1/4 cup cheese; bake an additional 1 minute or until cheese melts. Cut frittata in half; top each serving with 2 tablespoons sour cream.