Search and search and you probably won't find many decent lamb recipes for your smoker. Why? Because people think lamb is either too hard to make or because they haven't had lamb like this. Think of the most succulent steak you've ever had - something you can cut with a fork then you're in the ballpark for this savory, tender rack of lamb recipe.
When smoking lamb, most sources will recommend to stick with a lighter flavored wood. I would agree. Try alder or mix alder with a little grapevine or cherry. You could also try oak. It is a pretty versatile wood that mixes well with other woods.
This recipe was inspired by an old newsletter from the December 2008 issue of Hot off the Grill. 
Recipe
Yield: serves 10
Prep time: 15 minutes
Cooking time: 45 minutes
Ingredients
4 racks of lamb, trimmed and frenched
9 cloves garlic, minced
6 tablespoons fresh rosemary, finely chopped
2 large lemons, zested
4 teaspoons coarse ground black pepper
4 teaspoons coarse sea salt
1/2 cup olive oil (brushed on the meat)
Pull the lamb out while you warm up the grill to 325°F. If the racks are vacuum packed be sure to rinse them with cold water and some white vinegar. You can just pour some on a paper towel, run the rack under cold water and then wipe it down with the towel. Then rinse again and pat dry.
Trim and french the ribs. Be sure to trim the fat as much as you can since we'll be smoke-roasting it won't just melt away like baby back ribs. Liberally brush the racks with the olive oil. Mix all the ingredients for the wet rub in a bowl and about couple tablespoons of the rub everywhere except the sides. To keep the bones from becoming brittle wrap them with pieces of tinfoil.
Place the lamb racks on your smoker bone-side down. Let them cook for 30 minutes without opening the grill and then keep a close eye on the temperature for the next 5-15 minutes. You DO NOT want to overcook lamb. Pull them off between 135-140°F. And don't overcook them!! Remember since we're smoke-roasting the meat will come up to temperature awfully quick and these little petite racks don't take any time at all.
Cover the racks with a sheet of tinfoil and a towel to let the meat rest. Then chop the ribs by inserting a knife between the rib bones and cutting downward. These go well with a apple-mint jelly or a compound butter. I served these with a chive lemon butter - whip 3 cubes of softened butter with a bunch of chopped chives and the zest of 1 lemon (or even lemon salt).