Spray a non stick skillet with cooking spray. Saute onion, peppers, mushrooms and prosciutto over medium heat until tender; set aside. Spray a 10 inch (25 cm) non stick skillet with cooking spray. Beat eggs with water; season with salt and pepper. Stir in parsley and vegetable prosciutto mixture. Pour into skillet and lower heat to medium low. As mixture sets at the edges, with spatula, gently lift cooked portion to allow uncooked egg to flow underneath. Cook until bottom is set and the top is almost set, about 4 minutes. Cover with lid or foil for 2 to 3 minutes or until eggs are set. Cut into wedges to serve.