With marinades, the intent is to increase the flavor as well as the tenderness, so don't be shy with your favorite seasoning.
Ingredient list (in approximate order of how much I used):
Extra Virgin Olive Oil (EVOO)
Lemon juice (and I also used some shaved leomon rind which gives great flavor)
Salt (soy sauce already gave us some salt)
Combine the ingredientes and place in a food processor.
The lamb... Trim the excess fat and butterfly the meat (slice it further so you can spread it out on the grill). You don't want a big "roast", you want the meat to be of even thickness so that it cooks evenly. I wish I'd have taken a picture to show where I sliced it, but hey, part of the fun is trying something new and figuring it out on your own.
Place the lamb and the marinade in a zip-lock bag and let marinate overnight. Some recipes say you can marinate for a few hours, and I'm sure that is great, but I love the stronger flavor that an overnight marinade provides.
Sear it on both sides against the hottest part of the grill. Don't leave it alone for too long due to the fat in the olive oil.
If you have your coals spread out evenly and the fire isn't too hot, you can cook this directly over the charcoal with minimal flare-ups.
Grill to medium rare (pull off the grill at about 125 degrees). Let it sit for a few minutes then slice it against the grain (about 1/2 inch slices or thinner is good), on an angle. Great with Pinot Noir or Zinfandel (yes, red).