How to Make It
Light a grill. Set the lamb fat side down on a work surface. Using a large, sharp knife and holding it parallel to the work surface, cut through the thickest part of the meat, leaving it attached at one side so it can be opened like a book.
In a small bowl, mix the cumin with the paprika, 2 teaspoons of salt, 1/2 teaspoon of pepper and 1 tablespoon of the olive oil. Rub the cumin paste all over the lamb.
In a large bowl, toss the peppers with the remaining 1 tablespoon of olive oil and season with salt and pepper. Grill the lamb and peppers over moderately high heat, turning once, until the meat is medium and the peppers are crisp-tender, about 8 minutes per side. Transfer the lamb to a cutting board and let rest for 10 minutes. Transfer the peppers to a bowl and cover with foil.
In a medium bowl, mix the yogurt with the olives, parsley and garlic and season with salt and pepper. Slice the lamb and serve with the grilled peppers and olive-yogurt sauce.