In a deep nonstick 12" skillet, cook sausage over medium-high heat, stirring occasionally, until browned on all sides, about 5 minute.
Reduce heat to medium. Discard all but 2 T sausage fat. Add garlic, pepper and onion to sausage in skillet; cook, covered, stirring occasionally, until vegetables are tender, 10 minute Stir in whole tomatoes, tomato puree and salt; bring to a boil over medium heat, breaking up tomatoes with side of spoon. Reduce heat to low; cover and simmer 10 minute.
Meanwhile preheat oven to 400 degrees F. In a large pot of boiling salted water, cook pasta 2 min less than cooking time recommended on label.
Drain pasta and return to pot; stir in sausage mixture to coat. Add mozzarella and toss to combine. Transfer pasta mixture to an ungreased 9x13" baking dish and spread it out evenly; sprinkle with grated cheese.
Bake, uncovered, until top browns and sauce is bubbling, 20 to 25 minute Let stand 10 min before serving.