In a large nonstick skillet coated with cooking spray, saute the onion, the bell pepper, the mushrooms, and the prosciutto over medium heat until tender. Set aside. In a bowl beat together the eggs and the water, and season with salt and pepper. Stir in the parsley and the mushroom mixture. Pour the egg mixture back into the skillet, and reduce the heat to medium-low. As the mixture sets at the edges, gently lift the cooked portion with a spatula to allow the uncooked egg to flow underneath. Cook until the bottom is set and the top is almost set, about 4 minutes. Cover with foil, and cook for 2 to 3 minutes more, or until the eggs are set. Cut into wedges and serve.