Place the seeds in a coffee grinder and grind to a powder. Place the mixture on a plate. Season the loin with salt and pepper to taste and dredge on all sides with the spice mixture. Heat the oil in a medium skillet over high heat until almost smoking. Sear the lamb on all sides until golden brown. Transfer the lamb to the oven and roast for 8 to10 minutes for medium-rare doneness. Remove and let rest.
Place the skillet on top of the stove over high heat. Remove all but 2 tablespoons of the fat. Add the shallots and cook until soft. Add the wine and cook until reduced by 3/4. Add the stock and cook until reduced by half. Whisk in the mustards and season with salt and pepper to taste. Remove from the heat and stir in the mint.