Cut a horizontal pocket through the centre of each pork steak.
Combine the garlic, sage and oil in a small bowl, then rub this mixture all over the outside and inside of the pork steaks. Place in a shallow dish, cover with clingfilm and leave to marinate in the refrigerator for at least 30 minutes or overnight.
Season the outside and inside of the pork steaks with salt and pepper, then place on a baking sheet lined with foil. Cook under a preheated very hot grill, about 10 cm (4 inches) from the heat, for 5 minutes. Turn the pork steaks over and cook for another 5 minutes or until cooked through and golden. Serve with sweet potato mash, or ordinary mash if you prefer.