Peel the garlic and press it through a garlic press. Peel and finely dice the onions. Wash and chop parsley. Carve pepperoni lengthwise, remove seeds and chop finely. Heat 1 tablespoon of oil.
Fry garlic, 2 diced onions, half parsley and pepperoni for 2 minutes. Crush canned tomatoes and add them with the juice. Season with salt and pepper and simmer for 20 minutes. Knead tartar, remaining onion and parsley, grated parmesan and breadcrumbs.
Season with salt and pepper and form small balls from it. Heat 1 tablespoon of oil. Fry the meatballs for 3 minutes. Add to the tomato sauce and cook for another 10 minutes. Cook the spaghettini in boiling salted water for about 8 minutes until al dente.
Serve with tomato sauce and meatballs in portions. Serve garnished with pickled peppers, parsley and parmesan slices.