The frittata makes for a quick supper or hearty breakfast, and is great leftover, too. Make it your own with your choice of fillings.
Heat oil over medium heat in a large cast iron skillet (or other oven-safe pan). Add vegetables and saute for 3-4 minutes, stirring occasionally.
While the vegetables are cooking, crack eggs into a bowl, and whisk together with the milk, salt, and pepper.
Preheat broiler. Pour eggs into pan, and allow to set for 4-5 minutes. Use a silicone spatula to loosen edges around the pan about half way through.
Turn off the burner. Sprinkle Parmesan on top, and put the pan under the broiler for 4-5 minutes. The frittata will puff up and begin to brown lightly on top. The frittata is done if no liquid egg runs out when the center is pierced with the tip of a knife. Allow the frittata to sit for 5 minutes before cutting.