If sautéing vegetables, heat 1 tablespoon olive oil in an 10" cast iron (or other oven-safe) skillet over medium-low and cook vegetables. If not sautéing vegetables, heat olive oil alone.
Whisk together eggs, milk, salt, and pepper. Pour into skillet and cook for 5-6 minutes until bottom is set. Sprinkle of fresh vegetables and cheese. Transfer to the oven and bake for another 10-12 minutes until puffed up, doesn't jiggle, and is slightly browning. Remove and let cool slightly before serving.
Notes
*Often I'll make this recipe for 2 people by cutting the recipe down to 4 eggs and 1/4 cup milk. Adjust the cooking time down to 8-10 minutes.