Choose your favorite sauce for this quick pizza. Most supermarkets have a good selection of jarred pasta and pizza sauces ranging in flavor from simple marinara to roasted pepper.
Remove and discard casings from sausage. Cook sausage in a large skillet over medium-high heat 8 minutes, stirring until meat crumbles and is no longer pink. Push meat to outer edges of pan; add 1 Tbsp. oil. Add onion and garlic; cook 5 minutes or until onion is softened. Remove from heat; stir in pizza sauce and next 3 ingredients.
Cut bread in half lengthwise using a serrated knife, and scoop out center of each bread half, leaving a 1/2" border; discard scooped-out bread or reserve for making breadcrumbs.
Spread 1/3 cup ricotta down center of each bread half. Top each evenly with sausage mixture, mozzarella, and Parmesan cheese. Drizzle pizzas evenly with remaining 1 Tbsp. oil. Place pizzas on a lightly greased baking sheet.
Bake at 425° for 6 minutes or until cheese is melted and pizzas are thoroughly heated.