Whisk eggs, milk, cheese, parsley, salt and pepper together in a large bowl.
Heat the olive oil in a 10 inch nonstick skillet over medium heat. Add onion, zucchini, asparagus, and yellow squash to pan and sauté for 2 minutes. Add a pinch of salt.
Pour the egg mixture into the skillet and let cook on medium-low heat for 10 to 12 minutes. When the center is almost set, place skillet in a heated broiler to finish cooking and lightly brown the top.
Loosen the frittata with a spatula and slide it onto a serving plate… cut like you would a pizza.
