Preheat oven to 375°.
Press Greek Baking-Powder Piecrust into a 10-inch quiche dish coated with cooking spray. Combine eggs and egg whites in a medium bowl; beat well with a whisk. Brush 2 tablespoons egg mixture over crust, and set remaining egg mixture aside. Bake at 375° for 7 minutes; cool on a wire rack.
Place a large nonstick skillet coated with cooking spray over medium heat until hot. Add onion, bell pepper, and 1/4 teaspoon salt; saute 10 minutes or until lightly browned. Add zucchini, garlic, and water; saute 10 minutes or until vegetables are tender. Stir in thyme. Spoon zucchini mixture into prepared crust.
Add milks and 1/4 teaspoon salt to remaining egg mixture in bowl; beat well. Pour egg mixture evenly over zucchini mixture; sprinkle with cheeses. Bake at 375° for 45 minutes or until knife inserted near center comes out clean.