1. In a large measuring cup, combine broth with 1 cup water. Set aside.
2. Heat oil in a large pot over medium heat; add onion and cook for 3 minutes, stirring occasionally. Add crumbled sausage and mushrooms and cook for 5 minutes, stirring occasionally. Stir in rice and cook for 1 minute; add wine and cook 1 minute until liquid evaporates.
3. Add 1/2 cup of the broth-water mixture. Stir frequently and when broth is almost absorbed add another 1/2 cup. Continue adding broth-water mixture in 1/2-cup increments, stirring until rice is tender, about 28 minutes.
4. Stir in crushed tomatoes and black pepper. Gradually wilt in spinach.
5. Remove risotto from heat and stir in cheese. Spoon into a large warm bowl and serve immediately. Garnish with additional cheese, if desired.