Melt butter in skillet over medium heat. Add onion and cook until tender and beginning to brown. Add mushrooms, and cook for 2-3 minutes, stirring every 30 seconds. Add peppers, zucchini, and tomatoes. Mix well. Add parsley. Cook a few minutes until vegetables are tender but not overcooked. Remove from heat. Serve over hot rice or noodles. Serves 3-4.