Heat a large saucepan or pot over medium-high heat. Add the ground beef and break it up with a meat masher or wooden spoon. Cook until browned, about 6–8 minutes, then drain excess grease.
Add the salt, black pepper, chopped yellow onion, and minced garlic to the browned beef. Stir in the Italian seasoning, dried parsley, garlic powder, red pepper flakes (if using), Worcestershire sauce, sugar, and dried basil. Cook until the onions are soft and translucent, about 4–6 minutes.
While the onions cook, microwave 1 cup of hot water in a microwave-safe bowl for 2–3 minutes. Crumble in the Knorr tomato bouillon cube and stir until fully dissolved.
Stir in the two 15-ounce cans of tomato sauce, the tomato paste, and the hot water with dissolved bouillon to the pot. Mix well and bring the sauce to a gentle boil.
Reduce heat to low, cover, and simmer the sauce for 30 minutes, stirring occasionally.
Meanwhile, cook the spaghetti noodles according to the package directions, then drain.
Serve the sauce over the cooked spaghetti noodles.