Preheat your oven to 350°F (175°C).
Grease a muffin tin or line with paper liners.
In a large bowl, whisk together the eggs.
Add salt and pepper to the eggs, mixing well.
Stir in the diced vegetables and cheese.
If using, add the cooked meats to the mixture.
Pour the egg mixture evenly into the muffin tin.
Fill each cup about 3/4 full.
Bake in the preheated oven for 20 minutes or until set.
Allow to cool slightly before removing from the tin.