1. Spray inside of 4-quart slow cooker with cooking spray. Heat oil in large skillet over medium-high heat. Add mushrooms; cook 3 minutes, stirring occasionally. Add spinach; cook 3 minutes more or until mushrooms are tender and spinach is wilted, stirring occasionally. Stir in undrained tomatoes, tomato sauce, Italian seasoning and salt. Bring to a boil. Reduce heat and simmer 3 minutes, stirring occasionally. Meanwhile, combine ricotta cheese, 1/4 cup Parmesan cheese and pepper in small bowl; set aside.