This easy dinner party recipe brings the heat, literally. Shishitos are a fun game of pepper roulette—most are mild, but sometimes you get a fiery one. Make day-of cooking easier, and add some flavor too, by taking the time to season the lamb. Letting it marinate overnight will pump up the flavor and take time off pre-dinner prep. Mostarda might sound like mustard, but it’s actually more like a cross between a compote and a relish made with mustard seeds. This make-ahead plum version cuts through the rich lamb and tames any spiciness from the shishitos. Serve with a spicy red wine or a dry rosé.