Pat dry the lamb steak. Roughly grate the onion and finely grate the garlic and mix both with the olive oil, lemon juice, oregano and pepper. Spread the mixture over both sides of the lamb and place all in a box or freezer bag in the fridge for at least an hour but all day/overnight better. Turn over at least once part way through.

When ready to cook, heat the grill or griddle pan, shake off any excess marinade mixture and grill for a few minutes on each side until it reaches your preferred level of doneness (exact times vary depending on the grill heat, thickness and if you prefer slightly underdone, as I'd recommend, or not).