I would do it hot and fast if it's a leg, rack, or a saddle (loin) or if it is shoulder of Lamb I would go low and slow as it is fatty and will take the low and slow to render the fat out.
For leg or shoulder, I like to slit it all over, then put garlic into one third of the slits, rosemary into one third of the slits and sage into the other third, then give it a cover of Sea salt and black pepper.
The other thing is do it to medium rare if you like Lamb, much past 145 internal and it can start to dry out.
I like to serve it with mint sauce, (from my British heritage).
1-cup malt vinegar
1-cup fresh finely chopped mint
1-tablespoon sugar (or to taste)
Warm the vinegar in a pan, stir in the sugar until it dissolves, remove from the heat allow to cool, add the finely chopped fresh mint, stir and serve with the lamb.
"There's no such thing as a little garlic" A. Baer
KCBS certified barbecue judge.