Preheat the oven to 375°F (190°C) and grease a muffin tin with butter or non-stick spray.
In a bowl, whisk together the eggs, milk, salt, and black pepper until well combined.
Chop the vegetables and chicken sausage into small pieces.
Fill each muffin cup about halfway with the vegetable and sausage mixture.
Pour the egg mixture evenly over the vegetables, filling each cup about ¾ full.
Sprinkle shredded cheese on top of each muffin.
Bake for 18-20 minutes, or until the eggs are set and slightly golden on top.
Let cool for a few minutes before removing from the tin. Serve warm or store for later!