In a food processor combine the marinade ingredients and process until an almost smooth puree forms. Place the lamb, opened flat, in a large glass baking dish or on a sheet pan. Spread the marinade evenly all over both sides of the lamb. Cover with plastic wrap and refrigerate for 8 to 24 hours. Allow the lamb to stand at room temperature for 45 minutes to 1 hour before grilling (do not scrape the marinade off the lamb).
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Preparing Boneless Leg of Lamb
Cut off the thick stalks and the root ends from the fennel bulbs and discard. Finely chop and reserve the fronds for garnish. Cut each fennel bulb lengthwise in half and cut out the thick triangular core at the bottom. Cut each half into ⅓-inch slices. In a large bowl combine all the cut vegetables. Add ¼ cup oil, the salt, and pepper and toss gently, being careful not to break the vegetables. If the vegetables seem dry, add one more tablespoon oil.
Prepare the grill for direct cooking over medium heat (350° to 450°F).
Brush the cooking grates clean. Grill the lamb, fat side down first, over direct medium heat, with the lid closed, until an instant-read thermometer inserted into the thickest part of the meat registers 125° to 130°F, 30 to 45 minutes for medium rare, turning once after 20 minutes.
About 15 minutes before the lamb is done, prepare the couscous. In a large, heavy saucepan over medium-high heat on the stove, heat the oil. Add the shallots and garlic and sauté until golden and tender, about 5 minutes. Stir in the cumin, turmeric, salt, and pepper. Add the chicken broth and bring to boil. Stir in the couscous. Remove from the heat, cover with the saucepan lid, and let stand 5 to 10 minutes (keep the couscous covered to keep warm).
Related Grill Skills
Remove the lamb from the grill, tent with aluminum foil, and let rest for 10 to 15 minutes. Maintain the heat of the grill.
While the meat is resting, grill the vegetables over direct medium heat, with the lid closed, until tender and lightly charred on the outside, turning occasionally. The fennel and squash will take 10 to 12 minutes, the peppers will take 6 to 8 minutes, and the zucchini will take 3 to 5 minutes. Remove from the grill as they are done.
Cut the lamb crosswise into slices. Spoon the couscous on half of a large platter and the vegetables on the other half. Top the couscous with ½ cup of the chopped mint and sprinkle the fennel fronds over the vegetables. Arrange the lamb slices on the couscous. Top the lamb with the remaining ¼ cup chopped mint. Drizzle the lamb with any accumulated juices. Serve warm.