1. Heat a large skillet over medium-high heat. Add sausage; sauté for 6 minutes, stirring to crumble. Remove sausage from pan; drain. Wipe pan clean; return to medium-high heat. Add oil to pan; swirl. Add onion, and sauté 4 minutes. Add garlic; sauté 1 minute. Stir in sausage, marinara, and 1/3 cup water; bring to a boil. Reduce heat; simmer 20 minutes.
2. Bring remaining 2 cups water and milk to a boil in a medium saucepan over medium heat; reduce heat to low. Gradually add polenta, and cook for 3 minutes or until thick, stirring constantly. Remove from heat; stir in cheese and pepper. Serve with sausage mixture; top with parsley.