1Preheat oven to 425ºF.
Over medium-high heat, melt butter in a 10 inch fry pan (non-stick or a pan that is oven safe). Saute mushrooms for 4-5 minutes. Slice zucchini in half longways, then slice into half moons. Add zucchini to mushrooms in pan ,add green onions.Season with salt and pepper, cook an additional 1-2 minutes.
While the veggies are cooking, mix 4 eggs in mixing bowl with cheese,salt and pepper. Slowly pour over the veggies in pan. Let cook over medium heat for 2 minutes. Transfer to oven for 10 minutes.
Remove pan from oven and use a rubber spatula to loosen the frittata around edges and underneath. Invert plate over top of a plate and flip. Place another plate on top and flip (to make your frittata right side up). Slice into wedges and sprinkle with parsley just before serving.