In a small bowl, combine 1/4 cup soy sauce, lemon juice, mustard powder and the spice powder.
Place the salmon in a shallow dish, brushing both sides of the fish with the soy mixture. Cover the dish with plastic and refrigerate for 1 hour.
Preheat the broiler.
Spray a medium skillet with cooking spray and heat it over medium heat. Add the sesame seeds. Sauté until the seeds are golden, 1 to 2 minutes. Transfer the sesame seeds to a plate.
Spray the skillet again.
Sauté the carrots and leek until they are crisp, but tender, about 5 minutes. Add the water or broth, remaining soy sauce and sesame oil. Simmer until most of the liquid evaporates, about 10-15 minutes.
Meanwhile, place the salmon on a broiler pan. Broil, 4 inches from the heat, until the fish is cooked through, about 5 minutes.
Spoon the leek mixture evenly onto 4 serving plates and arrange the salmon filets on top. Sprinkle with sesame seeds.