Using ground nuts and seeds on a cutlet instead of breadcrumbs ups both the nutrition and flavor. Even better, walnuts contain omega-3 fatty acids , and flax seeds add a prebiotic punch.
Combine walnuts and flax seed meal in a shallow dish. Rub turkey cutlets with mustard, and sprinkle with ½ teaspoon of the salt and ¼ teaspoon of the pepper. Dredge turkey in walnut mixture, pressing to adhere.
Heat 1 tablespoon of the oil in a large nonstick skillet over medium-high. Add half of the cutlets; cook until lightly browned on 1 side, 2 to 3 minutes. Turn and cook until cooked through, 2 to 3 more minutes. Remove to a plate; cover with aluminum foil to keep warm. Repeat with remaining oil and cutlets.
Wipe skillet clean. Add carrots and 1/2 cup of the stock. Cook over medium-high, stirring occasionally, until carrots are slightly softened, 5 to 6 minutes. Add leeks, apple, thyme, and remaining ¼ cup stock, ½ teaspoon salt, and ¼ teaspoon pepper. Cook, stirring often, until apple is softened, 3 to 4 minutes. Add butter, and cook until leeks begin to caramelize, about 3 more minutes. Serve vegetables with turkey, garnished with additional thyme.