Preheat the oven to 375°F (190°C). Lightly grease a baking dish with olive oil and set aside.
Chop and measure the vegetables into small, uniform pieces. Add them to a large mixing bowl.
6 large eggs
In a separate bowl, whisk together the eggs, milk (if using), salt, and pepper until well combined and slightly frothy.
6 large eggs
Pour the beaten eggs into the mixing bowl with vegetables. Add the shredded cheese and stir until evenly incorporated.
6 large eggs
Pour the mixture into the prepared baking dish. Spread evenly with a spatula.
6 large eggs
Bake in the preheated oven for 20-25 minutes, or until the top is golden brown and the casserole has puffed up slightly. Inspect the edges, which should be crispy and bubbling slightly around the sides.