This marinade sounds like it would overpower the mild flavor of grilled lamb, but it will not. I also seam out a leg of lamb instead of buying butcher-sliced, but any thick slices will do. Even lamb chops could be used for this recipe. The picture below is a seamed leg of lamb. The three center pieces are the ones used for this recipe.
2 to 4 pieces of lean lamb, 1 inch thick
1/4 cup olive oil
4 large cloves garlic, minced
3 tablespoons chopped fresh rosemary
Salt and pepper to taste
Combine the oil, garlic, and rosemary in a small saucepan and simmer for3 minutes over medium-low heat. Turn off the heat and let stand until cooled to room temperature. Combine the seasoned oil and lamb in a zip-top plastic bag. Zip the bag almost closed, expel as much air as possible, and zip the bag fully closed. Refrigerate until the next day. Remove the lamb from the refrigerator and place the bag in warm water for 1 hour before grilling. Prepare the grill for direct cooking over a very hot fire (600°F). Remove the lamb from the marinade and brush off the excess.
Grill the meat directly over the heat, lid closed, for 2 1/2 minutes per side for medium rare.