Preheat the grill to high. Put the turkey steaks on a chopping board and cover with clingfilm, then bash with a rolling pin until roughly 1cm (½in) thick. Cut each steak in half and set aside.
Heat the oil in a large frying pan. Grind the cumin and fennel seeds in a pestle and mortar, then transfer to a small bowl. Add the chilli powder and flour and mix to combine. Dip the steaks in the beaten egg, shake off any excess and then dip in the flour mixture. Fry in batches for 3 minutes on each side, until golden.
Transfer the cooked steaks to a baking tray and top each with a little mozzarella. Cook under the grill for 3-4 minutes, until the mozzarella is melted and just turning golden. Cut into a thick portion of turkey and check that it is cooked through, with no pink showing.
To serve, divide the lettuce between 4 burger buns and top with two pieces of turkey and some slices of tomato.
Freezing and defrosting guidelines
In order to enjoy optimum flavour and quality, frozen items are best used within 3 months of their freezing date. Always defrost and heat thoroughly before eating. For more tips on freezing and defrosting food, read our article Love Your Freezer.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.