Preheat the oven to 350°F (175°C) and lightly grease a muffin tin or line it with muffin liners.
Whisk the egg whites in a bowl until slightly frothy. Add salt and pepper to taste.
Prepare the muffin cups by evenly distributing the diced vegetables, shredded cheese, and cooked meat into each section.
Pour the egg whites over the ingredients, filling each muffin cup about ¾ full.
Bake for 18–20 minutes or until the muffins are set and lightly golden.
Let them cool for a few minutes before removing them from the muffin tin. Serve warm or store for later use.