Prepare the Marinade: Mix olive oil, oregano, salt, and the juice and zest of lemons in a bowl.
Marinate the Lamb: Ensure lamb rumps are fully covered in the marinade and refrigerate for 1 to 2 hours, maximum 3 hours.
Grill Setup: Set up the grill with charcoal on one side and no charcoal on the other.
Start Grilling: Begin grilling with the fat side down over the hot side to render the fat, then move to the cooler side to avoid flames.
Cook to Desired Doneness: Cook to an internal temperature of about 48°C for medium, flipping often for an even cook.
Rest the Meat: Let the lamb rest for 5 to 10 minutes before carving.
Serve: Carve against the grain and serve with a classic Greek salad and extra olive oil.