Cook beef and Italian seasoning in a large skillet over medium-high heat, stirring until beef crumbles; drain. Combine spaghetti sauce and water in a small bowl.
Place 4 uncooked noodles in bottom of a lightly greased 5-quart electric slow cooker. Layer with half each of beef mixture, spaghetti sauce mixture, and mushrooms.
Spread ricotta cheese over mushrooms. Sprinkle with 1 cup mozzarella cheese. Layer with remaining noodles, meat, sauce mixture, mushrooms, and mozzarella cheese. Cover and cook on HIGH setting 1 hour; reduce heat and cook on LOW setting 5 hours.