Apologies for the late reply.
My wife is Croatian/American and the Croatians love their barbecued lamb. It's simple: trim, rub with salt and butter, insert cloves of garlic liberally. Butterfly if you want ( I generally bone and tie it) or just put on a spit and roast over coals. In addition some people like to rub with rosemary and or thyme, but we are purists. Cook to an internal temp of 145-155 (depending on whether your taste is for medium rare or medium), let rest for 15 minutes carve and serve. Have lots of fresh sliced bread, green onions and garlic roasted potatoes and red wine on hand. We make this every Easter, along with a traditional Croatian Easter sausage," nadev" (made from bread, eggs, green onion tops, smoked pork butt, ham, salt pepper, spices all stuffed in a large casing and simmered in boiling water for up to 4 hours).
Have you posted any pics yet? I would love to see how it turned out.