How to Make It
In a food processor, combine the cucumbers, mint and 1/2 teaspoon of kosher salt. Pulse until minced but not pureed. Transfer the cucumber mixture to a coarse strainer set over a bowl. Let drain in the refrigerator for at least 1 hour and up to 3 hours.
Preheat the oven to 500°. In a small skillet, combine the cinnamon, sesame, fenugreek, cumin, mace, cardamom, red pepper and clove. Toast the spices over moderately high heat until fragrant, about 2 minutes; shake the pan frequently. Transfer the spices to a plate to cool. Coarsely grind the spices in a spice grinder or mortar. Transfer the spices to a small bowl and stir in the nutmeg.
Using a sharp knife, score shallow X marks in the fat of the lamb racks. Rub the spice mixture over both sides of the racks. Heat 2 large ovenproof skillets over high heat for 2 minutes. Add 1 tablespoon of the oil to each skillet. When the oil is very hot, add a rack of lamb to each skillet, fat side down. Cook the lamb until browned, about 2 minutes. Turn the racks over and cook for 2 minutes on the bony side. Turn the racks again, fat side down, and transfer the skillets to the oven. Roast the racks for 15 minutes for medium rare. Remove from the oven and cover loosely with foil. Let the racks rest for 10 minutes.
Transfer the cucumber relish from the strainer to a bowl; season with kosher salt and black pepper. Carve the lamb into chops and serve with the relish.