Preheat broiler. Whisk together eggs, egg whites, and cheese in bowl; season with salt and pepper, if desired. Set aside.
Heat 1 Tbs. oil in 10-inch ovenproof skillet over medium-high heat. Add shallot, and sauté 2 minutes. Add garlic; sauté 30 seconds. Add zucchini; sauté 2 minutes. Stir zucchini mixture into egg mixture; set aside. Add squash blossoms to skillet, and sauté 30 seconds. Remove squash blossoms from skillet and set aside.
Heat remaining 1 Tbs. oil in same skillet over medium-low heat. Add egg mixture to skillet. Arrange squash blossoms in circle on top. Cover, and cook 10 minutes, or until set.
Uncover skillet, and transfer to oven. Broil 3 minutes, or until top of frittata is golden. Slide frittata onto cutting board, and slice into 8 wedges. Serve right away.