1/2 cup chopped fresh Italian flat leaf parsley
1/3 cup chopped scallions
1/2 cup chopped fresh mint leaves
1/2 cup fresh lemon juice
2 teaspoons grated lemon peel
1 cup olive oil, preferably extra-virgin
2 teaspoons dried crushed red pepper flakes
3 1/2 teaspoons coarse salt
1 1/2 teaspoons freshly ground black pepper
1 (4 1/2 to 5-pound) butterflied lamb shoulder or leg
1 tablespoon minced garlic
Nonstick cooking spray
Stir the first 6 ingredients and 1 teaspoon red pepper flakes in a large bowl to blend. Whisk in 1 1/2 teaspoons of salt and 1/2 teaspoon of black pepper. Set the mixture aside. Place the lamb in a 15 by 10 by 2-inch glass baking dish. Rub the minced garlic, remaining 2 teaspoons of salt, 1 teaspoon of black pepper, and remaining 1 teaspoon red pepper flakes all over lamb. Pour 1/2 cup of spiced oil mixture over the lamb, turning the lamb to coat evenly. Use immediately, or cover the dish with plastic wrap and refrigerate up to 1 day.
Spray the grill rack with nonstick spray and prepare the barbecue (medium-high heat). Grill the lamb until a meat thermometer inserted into the thicker parts registers 130 degrees F for medium-rare, turning occasionally, about 40 minutes. Transfer the lamb to a work surface and let rest 15 minutes.
Cut the lamb across grain into thin slices. Arrange the lamb slices on a platter.