Mix together the turkey, one of the onions, the anchovies, breadcrumbs and a little salt and pepper in a bowl. Divide the mixture into 8 pieces and shape into flat patties.
Heat 2 tablespoons of the oil in a large frying pan and fry the patties for 8 minutes, until golden on both sides. Transfer to a plate. Add the remaining oil and onion to the pan and fry gently for 5 minutes. Stir in the tomatoes, tomato paste, oregano, sugar and a little salt and pepper and bring to a simmer.
Return the patties to the pan, pushing them down into the sauce. Cook gently, uncovered, for 15 minutes until the patties are cooked through.
Place the mozzarella slices on top and season with plenty of pepper. Cook under a preheated moderate grill until the cheese melts. Serve with warmed olive ciabatta, if liked.