Preheat the oven to 350°F (175°C). Grease a muffin pan. Set aside.
In a large bowl, whisk the eggs and black pepper. Stir in the Parmesan cheese and set aside.
In another large bowl, add the tomatoes, prosciutto, spinach, feta, mushrooms, and onion, and mix well. Spread the mixture evenly between the 12 muffin cups.
Pour the egg and cheese mixture over the top so that each cup is almost full.
Bake for about 20 minutes, until set. Let cool for a couple of minutes before freeing any stuck edges with a butter knife. Enjoy!