Preheat broiler. In a large broilerproof skillet cook onion and garlic in 2 tablespoons hot oil until onion is just tender.
Meanwhile, in a bowl, beat together eggs and half-and-half. Stir in feta cheese, roasted sweet pepper, olives (if desired), basil, and black pepper. Pour egg mixture over onion mixture in skillet. Cook over medium heat. As mixture sets, run a spatula around the edge of the skillet, lifting egg mixture so uncooked portion flows underneath. Continue cooking and lifting edges until egg mixture is almost set (surface will be moist). Reduce heat as necessary to prevent overcooking.
In a bowl combine crushed croutons, Parmesan cheese, and the remaining tablespoon of oil; sprinkle mixture over frittata.
Broil 4 to 5 inches from heat for 1 to 2 minutes or until top is set and crumbs are golden. Cut frittata in wedges to serve. If desired, garnish with fresh basil leaves. Makes 6 servings.