Best ever stuffed Zucchini Boats

Ingredients:
3 med. zucchini halved lengthwise
1 lb Italian sausage
1 sm onion  chopped
1 clove garlic crushed
1/3 C bread crumbs
1/4 C Parmesan
1 C shredded Mozzarella
Cook Zucchini in boiling water for 10 minutes. Drain, then scoop out insides leaving 1/4" shell. Mash insides, drain well.  Put boats in shallow baking dish.  Remove sausage from casings, brown 5 minutes. Add garlic and onion, and saute until meat is cooked through and onions are tender.  Stir in Zucchini and bread crumbs. Spoon into boats.  Sprinkle with cheese.  Bake at 350 for 30 minutes