Place potatoes in a saucepan, and cover with water; bring to a boil. Reduce heat, and simmer 8 minutes or until tender; drain and set aside.
Place a nonstick skillet coated with cooking spray over medium-high heat. Add the onion, and cook 20 minutes or until deep golden brown, stirring frequently. Remove onion from pan, and recoat pan with cooking spray. Return onion to pan; stir in potatoes and 1/4 teaspoon salt.
Combine 1/4 teaspoon salt, parsley, and next 5 ingredients (parsley through garlic) in a bowl, stirring well with a whisk. Pour over onion mixture; sprinkle with cheese. Cook over medium heat 2 minutes or until slightly set. Wrap handle of skillet with foil; broil 3 minutes or until eggs are set and cheese is melted. Gently slide frittata onto a platter, and cut into 8 wedges.