If your meat is not already minced, whiz it up in a food processor to the required consistency and place it in a bowl. Use the food processor to turn the slices of bread into bread crumbs. Add the bread crumbs, dried oregano, cumin, coriander, chile, rosemary, and egg to the minced meat and season with a good pinch of salt and a good twist of black pepper. Mix well, and with wet hands, roll, and pat into meatballs the size and shape you want. (These can be cooked straight away or put on greaseproof paper, covered with plastic wrap and refrigerated for up to 1 day.)
Preheat the oven to 400 degrees F (200 degrees C/gas 6).
Preheat a thick-bottomed casserole to a very hot temperature. Add 3 to 4 tablespoons of olive oil, swirl around the bottom of the pan, and add your meatballs. Fry them until they are brown all over, being careful not to break them up but just moving the pan around so that all sides of the meatballs get nicely colored.
Meanwhile, to make your tomato sauce, fry the onion and garlic in a little oil. Add the dried oregano and tomatoes, rip in the basil leaves, season, and gently simmer for a few minutes. Turn the heat down, and pour over the meatballs with the mozzarella and grated Parmesan. Drizzle with olive oil and cook in the oven for about 15 to 20 minutes, until the cheese is golden. Serve with the cooked and drained spaghetti.