In a large saucepan over medium heat, cook spinach and a small amount of water, covered, until wilted (about 3 minutes), tossing once with a fork. Chop spinach and squeeze dry.
Melt the butter in a nonstick ovenproof medium size skillet over medium heat. Add in bell pepper, mushrooms and green onions; stir and sauté for three minutes.
Add in zucchini; stir and sauté for three additional minutes, or until the vegetables are tender. Stir in spinach.
In a mixing bowl, whisk eggs, milk, parsley, salt and pepper. Pour over vegetables in the skillet. Sprinkle feta cheese over the top.
Put skillet in a 350° oven; bake for about 25 minutes or until eggs are set. Let stand for 5 minutes. Cut into wedges and serve.