In a small bowl, whisk eggs and egg whites until combined. Mix in cheese, garlic powder, basil, salt, pepper, and nutmeg; set aside.
In a nonstick skillet with sloping sides, heat oil over medium heat. Add spinach; cover and cook 2-3 minutes or until spinach is slightly wilted, stirring once or twice.
Slice tomatoes. Spread spinach evenly in skillet and top with tomato slices. Pour in egg mixture. Reduce heat to low, cover, and cook 12-15 minutes or until egg mixture is set but still moist on top.
Cut frittata into wedges and serve with toast and grapes on the side.