Cut zucchini in half lengthwise. Scoop out pulp, leaving a 1/4 inch shell. Chop pulp and set aside. Place ground beef, onion and green pepper in small casserole. Cover and microwave at High for 1 to 2 minutes, stirring once until beef is browned. Drain. Add zucchini pulp, tomato sauce, 1 tablespoon Parmesan cheese, garlic powder and salt to ground beef mixture. Place half of the beef mixture in each zucchini shell. Sprinkle with remaining 1 tablespoon Parmesan cheese. Place stuffed zucchini on a microwave roasting rack. Cover tightly with heavy duty plastic wrap. Microwave at High for 1 1/2 minutes. Give dish a half turn, and microwave at High for 1 1/2 to 3 1/2 minutes or until filling is set and zucchini is fork tender.