This is a great prepare ahead frittata! I made this during my Sunday demonstration at Williams Sonoma and everyone loved it that came into the school.
Preheat boiler. In a large oven save sauté pan over medium heat. Add 1 tablespoon butter or coconut oil. Add the sliced mushrooms, tomato slices and red onion. Cook for 3-4 minutes until tomato is just softened.
Remove from pan and put on a plate. Wipe pan down with a paper towel.
In a bowl lightly beat eggs with 1 tablespoon water, salt and pepper. Stir parsley, scallions and the mushroom and tomato mixture.
Add remaining tablespoon of butter or coconut oil to the sauté pan over medium-low heat. Add the egg mixture and then cook for 5-6 minutes until golden underneath and nearly set. Use a rubber spatula to rub around the edges of the frittata.
Place pan under preheated broiler for 3-4 minutes or until just set and top is golden. Slide onto a board. Garnish the top with additional scallions Slice and Serve!