Wash the potatoes. Add them to a pot with water and boil for 10-15 minutes.
Allow to cool, remove the skin of the potatoes, and dice them into pieces.
Chop the onion, bell pepper, and mushrooms.
Heat a non-stick pan with olive oil, add the chopped onion, bell pepper, mushrooms, salt, and sauté.
Chop the spinach.
Combine the eggs, seasonings, milk, Parmesan cheese, cherry tomatoes, cooked potatoes, spinach, sautéed pepper, mushrooms, and onion in a large mixing bowl.
Preheat the oven to 375 degrees F. Preheat the sheet pan as well.
Transfer the mixture to the preheated sheet pan and place it in the oven. Bake for 15-20 minutes at 375 degrees F.
Allow to cool, and cut into pieces. Serve or store in an airtight container in the refrigerator for up to 5 days.