Cook ground beef and onions together in a large skillet until beef is browned and onions are soft. Drain fat.
Stir in spaghetti noodles, diced tomatoes, green pepper, water, mushrooms, chili powder, oregano, sugar, salt and garlic powder. Bring to a boil. Reduce heat to medium low and cover. Simmer for 30 minutes, stirring occasionally.
To serve, sprinkle with Parmesan cheese.
Notes
If you notice no liquid is left in the skillet and the noodles aren't cooked yet, add in another 1/2 cup of water.