In a large skillet on the stove-top, add the ground beef and diced onion and cook and crumble the ground beef until no longer pink and the onions are starting to turn translucent. Drain off excess cooking fat (if there is any).
Add cooked ground beef and onion mixture, cheese, tomatoes, corn, water and taco seasoning mix to a 5 to 6 quart slow cooker and stir to combine.
Cover and cook on LOW for 2 to 3 hours to allow the flavors to meld together and the cheese to melt.
Prior to serving, cook the spaghetti noodles on the stove-top according to the instructions on the package.
Serve taco spaghetti sauce either mixed into the noodles or spooned over top.