Preheat oven to 350°F.

Coat a 9-inch pie plate with cooking spray. Layer sweet potatoes in slightly overlapping concentric circles on bottom and upsides of plate, cutting slices in half to fit (rounded side up) around the sides. Coat potatoes with cooking spray. Bake in preheated oven for 20 minutes or until potatoes are slightly tender. Place pan on a wire rack. Increase oven temperature to 375°F.

Optional: grill chicken sausage or another lean protein to add to your quiche. Heat a large nonstick skillet over medium heat. Add oil and onion; saute 3 minutes. Add spinach; saute 3 minutes. remove from heat; cool.

Combine milk, salt, black pepper, crushed red pepper,eggs and egg whites in a medium bowl; stir with a whisk. Arrange spinach mixture in crust; pour egg mixture over spinach. Optional: add cut up sausage pieces. Sprinkle with feta. Bake at 375°F for 35 minutes or until egg mixture is set. Let stand 5 minutes; cut into wedges.