1. Put lamb in a large bowl. Add oil, garlic, spices, 1/2 tsp. salt, and 1/2 tsp. rosemary, tossing to coat evenly. Chill, covered, at least 1 hour and up to 1 day ahead.
2. Pulse croutons, lemon zest, and remaining salt and rosemary in a food processor into coarse crumbs.
3. Heat grill to high heat (450° to 550°). Grill lamb, turning once, 6 to 8 minutes for medium rare. Sprinkle with crumb mixture.
Note: Nutritional analysis is per chop.