Fry the onion and garlic in the oil until softened. Add the tomatoes and sugar, a little splash of vinegar and some seasoning, then simmer for 20 mins until really thick. Stir in the turkey and transfer to a baking dish. Heat oven to 220C/200C fan/gas 7.
Tear over the mozzarella in chunks, then scatter over the breadcrumbs with a bit more ground pepper. Bake for 20 mins until turkey is piping hot through, and the top is golden and bubbling. Eat with mash, jackets, rice or pasta