Preheat your oven to 350°F (175°C). Lightly grease a muffin tin with cooking spray or line with muffin liners.
In a mixing bowl, whisk together the eggs, milk, salt, and pepper until well combined.
Stir in the chopped vegetables and shredded cheese, if using, until evenly distributed.
Pour the egg and veggie mixture into the prepared muffin tin, filling each cup about 3/4 full.
Bake in the preheated oven for 20-25 minutes, or until the muffins are set and lightly golden on top.
Remove from the oven and allow the muffins to cool in the tin for a few minutes before transferring them to a wire rack to cool completely.
Once cooled, store the muffins in an airtight container in the refrigerator for up to 3-4 days.
Enjoy your delicious and nutritious egg and veggie breakfast muffins for a quick and satisfying meal anytime!