Preheat oven at 350° F.

Heat oil in an oven safe skillet over medium heat. Add onion strips and cook, stirring frequently, for 5 minutes or until onions are tender. 

Whisk together eggs, egg whites, milk, garlic salt, pepper and chives in a medium bowl. Stir into skillet with onions and cover. Cook for 7 minutes or until the edges of the frittata begin to set.

Remove stems and sepals from squash blossoms and discard. Arrange petals and pistils on frittata in a circular pattern. Top with cheese strips arranged in the same circular manner. Transfer skillet to oven and bake for 15 minutes or until the frittata cooks through. 

Remove from oven and let rest for 5 minutes. Slice and serve.