Combine the lamb, egg, tomato and Worcestershire sauces and breadcrumbs in a bowl. Mix well. Shape mixture into 16 meatballs.
Heat half the oil in a large deep frying pan. Cook the meatballs for 5 minutes, or until browned all over. Transfer to a plate.
Heat the remaining oil in the same uncleaned pan. Cook the onion and garlic, stirring, for 5 minutes or until softened. Add the tomatoes, pasta sauce and stock and bring to the boil. Reduce heat to low and simmer, covered, for 5 minutes.
Add the meatballs to the sauce and simmer, covered, for 10 minutes or until cooked through. Stir in the oregano and spinach and cook for 2 minutes or until spinach wilts.
Serve the meatballs and sauce on the spaghetti, sprinkled with Parmesan cheese.