Cut onion into large chunks and process in a food processor just until finely minced. Add onion to an 8 qt. cast iron pot with the olive oil. Cook just until translucent. If using garlic add to the onions 1-2 minutes before adding the rest of the ingredients.
While onions are cooking brown the hamburger meat in a medium saucepan with the 1/2 cup of water, drain and set aside.
Add all of the rest of the ingredients to the onions and cook covered on med/low heat for up to 3 hours. Stirring as needed. Add the hamburger in for the last 30 minutes.
Cook spaghetti noodles according to package directions. Drain and toss with the meat sauce.