Preheat oven to 350 F. Spray a quiche dish or 9" glass pie plate with non stick cooking spray.
In a quiche dish or 9" glass pie plate, add a layer of zucchini slices, then layer of cooked sweet potato cubes (I cooked mine in the microwave to save time), then another layer of zucchini slices. Season with a little salt and pepper.
In a mixing bowl, whisk together the eggs, milk, minced onion, minced garlic and salt and pepper. Pour over the veggies in the dish.
Bake in the preheated oven for 35-40 minutes, or until the eggs in the middle have cooked through.
Serve Sweet Potato Zucchini Frittata with fresh fruit and a glass of milk...a great weeknight "brinner."