On a cutting board using the flat side of a chef's knife smear together the garlic and salt to form a paste. Transfer garlic paste to a small bowl. Stir in chili powder, cumin, sugar, pepper, thyme, cinnamon, and allspice. Stir in enough olive oil to make a paste. Rub lamb chops all over with the paste. Cover and refrigerate lamb for 4 to 24 hours.
For a charcoal grill, arrange medium-hot coals around a drip pan. Test for medium heat above the pan. Place chops on grill rack over drip pan. Cover and grill to desired doneness, turning once halfway through grilling. Allow 16 to 18 minutes for medium rare (145 degrees F), or 18 to 20 for medium (160 degrees F). (For a gas grill, preheat grill. Reduce heat to medium. Adjust for indirect cooking. Grill as above.) If desired, serve with grilled tomatoes.