So, I finally did try to replicate your dish. And it was gooooood! Thanks for the idea.
I used the minion method with 6 lit coals. I banked all the coals on one side and covered the rest in foil. I used the baskets to hold the coals in place instead of putting them inside. It worked a lot better. I've never had that much control over the temperature of the kettle.
I put potatoes, carrots, garlic scapes, garlic cloves cut in 4 and onions.
Added the 4 pounds leg of lamb and herbs (rosemary and oregano), some coarse salt and cracked black pepper.
oregano and rosemary with the leg of lamb (about 4 pounds).
It cooked for a good half hour at 225F, and at 250 for another two hours and then I let it heat up between 250 and 300F for the last hour or so. I took it off the heat around 135F IT.
Ready to eat!
Wait! Where are the potatoes... and carrots... and onions... and...
Hummm, I didn't realise that cooking at that temp wouldn't cook the vegetables enough. I had to leave them in the kettle for a good hour while we were eating the meat. So it kind of turned into a two course meal...
This was my first time trying lamb on the BBQ (had cooked lots of it in the oven before though as it's one of my favorite meats) but it won't be the last.