Preheat oven to 350 degrees. Slice the mushrooms and dice the onions. In a saute pan that can be cooked in the oven (like a cast iron skillet), add the butter and turn the stove to medium-high heat. Add the sliced mushrooms and onions to the pan and let saute until tender. Add all of the seasonings to the mushroom/onions. In a mixing bowl and with a whisk, whisk together the eggs, milk, feta cheese and fresh parsley. Pour this egg mixture over the mushrooms and onions in the hot pan. Sprinkle the white cheese on top of the egg. Place the pan in the oven and bake for 20-25 minutes, or until the egg mixture is cooked and the top is golden and bubbly. Remove from the heat and garnish with fresh parsley and serve with your favorite salsa or sauces.