For the marinade, place olive oil, garlic, lemon juice, rosemary, sea salt and pepper together in a large non-metallic mixing bowl, whisking to combine. Place lamb in the marinade, cover and refrigerate for at least 4 hours, preferably overnight.

Heat a covered barbeque (eg. Weber) on high for 5 minutes, then reduce heat to medium-high. Place marinated lamb on the barbeque grill, cooking for 5 minutes on each side and closing the cover each time. Reduce the heat to low, leave cover down and cook for a further 15-20 minutes or until cooked to your liking. Remove lamb from the barbeque, cover with foil and rest for 15 minutes before serving.

NOTE: This recipe used a baby Weber Q but cooking times may vary, as all barbeques are different