For even simpler tacos, use 8 ounces of leftover shredded roasted chicken, pork, beef or turkey in place of the duck. More Incredible Duck Recipes
Preheat the oven to 350°. Season the duck breast with salt and pepper. In a small ovenproof skillet, cook the breast, skin side down, over low heat until the skin is golden brown, about 15 minutes; pour off the fat as it accumulates in the pan. Turn the duck breast over and transfer the skillet to the oven. Roast the breast for about 10 minutes, until an instant-read thermometer inserted in the thickest part registers 135°. Let the duck breast rest for 10 minutes, then slice it very thinly across the grain.
Meanwhile, in a mini food processor, combine the cilantro, pickled jalapeno, garlic and lime juice and pulse until the cilantro is finely chopped. Add the oil and puree until fairly smooth. Season with salt and pepper.
Arrange the tortillas on a work surface and top them with the duck, carrot, scallion and radish sprouts. Drizzle with the sauce, fold the tacos and serve right away.