Put the flour in a bowl with a little seasoning, beat the egg in another bowl with a splash of water. Tip the breadcrumbs and rosemary into another bowl, drizzle over 1 tbsp oil and rub together with your fingers until the breadcrumbs are a little moist. Dip the turkey steaks into the flour, dust off the excess, then dip in the egg followed by the breadcrumbs, pressing to help them stick. Put on a plate and chill while you prepare the sauce.
Heat the remaining oil in a large pan. Add the garlic and sizzle for 30 secs, then add the tomatoes. Season and bubble for 15 mins until the sauce is thick, adding a pinch of sugar if the taste is too sharp. While the sauce cooks, heat oven to 200C/180C fan/ gas 6, put the turkey steaks on a baking tray and bake for 10 mins, then remove from the oven, top with mozzarella slices and return to the oven for another 5 mins, until the turkey is cooked through and the cheese has melted.
Meanwhile, cook the spaghetti following pack instructions. Drain, then toss through the tomato sauce. Divide between plates and top with a turkey steak and a generous scattering of basil leaves.