Stir together ground meat, Italian seasoning, onion powder, garlic powder, chili powder, salt, and black pepper.
In the slow cooker, stir together spaghetti sauce, spinach, mushroom, and water.
Using a large disher or rounded tablespoons, shape meat into balls and drop in a single layer into the sauce mixture. Gently press them down slightly so they are mostly covered with sauce. Place the lid on the slow cooker, and cook on low 8 hours or high 4 hours.
About a half hour before serving, bring a large pot of lightly salted water to a boil, and cook pasta according to package instructions. While pasta cooks, gently stir meatballs into sauce. (Your meatballs might be a bit stuck together, but you can easily separate them with a spoon.)
Serve meatballs over cooked pasta, and top with cheese if desired.