Pour 2 quarts of cold water into a large bowl. Stir in 1/4 cup fine sea salt to create a brine. Once the salt has dissolved, submerge the duck breasts in the brine. Soak for 1/2 to 1 hour. Remove and rinse to remove the excess salt. Pat dry and using a sharp knife, score the skin with a cross- hatch pattern.
Meanwhile, start the glaze by roasting the unpeeled garlic on one side of a large skillet over medium heat, turning occasionally, until soft and blackened in spots, about 15 minutes; cool and peel. While the garlic is roasting, toast the chile pieces a few at a time on the other side of the skillet, pressing them down firmly with a spatula for a few seconds until they release a toasty aroma, then flip them, and press down the other side. Scoop the chiles into a small bowl, cover with hot tap water and let rehydrate for 30 minutes. Drain, reserving 1/3 cup of the soaking water.
Preheat the oven to 325 degrees.
In a food processor or blender, combine the chiles, the reserved soaking liquid, garlic, oregano, pepper, cumin, honey, vinegar and 1 teaspoon salt. Blend to a smooth puree, scraping down and stirring frequently. Press through a medium-mesh strainer into a small bowl. Set aside 1/2 cup of the glaze for the dressing.
Set a large (10-inch) skillet over medium high heat. Once the skillet is hot, place 2 of the duck breasts skin side down in the pan. Sear for 6 minutes until richly brown and the skin is crispy, flip and sear the underside for 1 1/2 minutes. Transfer to a wire rack set over a rimmed baking sheet and repeat this procedure with the remaining breasts.
Take the remaining pasilla glaze and brush the top of each of the duck breasts. Place the baking sheet into the center of the preheated oven and roast for 25 to 30 minutes or until the internal temperature reaches 125 degrees. Remove from the oven and allow to cool for 5 minutes before slicing.
Blend together the dressing ingredients along with 1 teaspoon salt.
Once the duck breasts have been sliced, plate up individual servings by arranging the mixed greens on the plate. Fan out the duck breast slices and sprinkle the radish slices,mango, avocado and corn over the top of the salad. Place two of the grilled scallions on each of the salads and drizzle on the dressing. Refrigerate any unused dressing in an airtight container.