Preheat oven to 400 degrees. Cut out the center of the bread leaving a 1-inch shell. Using your fingers, hollow out the bread to leave a 1" shell in the bottom also. Cut the bread you removed into rectangular pieces for dippers. Place the pieces on a baking sheet and drizzle with olive oil and toss. Place the bread bowl on a baking sheet. Bake both pans until the pieces are just toasted and the bowl is slightly dried out, approximately 20 minutes.
Remove the bread from the oven and rub the inside of the bread bowl with 1 clove of cut garlic.
Head 1 T. olive oil in a dutch oven. Add the onion and cook for 5 minutes. Chop the remaining garlic clove and add to the onion. Add the sausage, cook until brown, stirring to break into chunks. Add the pizza sauce. Cook for 5 minutes.
Pour the sauce into the bread bowl on the baking sheet. Top with the mozzarella and Parmesan cheese. Return the bread bowl to the oven. Bake until the cheese melts about 10 minutes.
Serve on a platter surrounded by the bread cube dippers.