1. Cook manicotti according to package instructions.
2. Combine broccoli, cauliflower and vegetable mix and cook in water for 10 minutes. Drain well and mash. Cook and mash sweet potato.
3. Combine matzoh ball mix with egg and oil. Combine all vegetables, matzoh ball mix and shredded cheese, mix well. Stuff one tablespoon filling into each manicotti.
4. Sauté onion in oil, arrange on the bottom of 9×13-inch pan. Sprinkle garlic powder, add water. Arrange manicotti over sauce.
5. Bake, covered, at 350 degrees Fahrenheit for 20-30 minutes until thoroughly reheated. Serve with mushroom sauce.