In a small bowl, combine the bread crumbs, horseradish, and 1/2 teaspoon of the oil. Coat the top of the flounder with the bread crumbs, using your fingertips to firmly press them in.
Heat the remaining oil in a medium nonstick skillet over medium-high heat. Add the flounder, bread crumb–side down. Cook 2 minutes or until browned. Turn and cook 2 more minutes or until cooked through.