Stir together the soy sauce, honey, 2 tablespoons mustard, ginger, garlic, and red pepper flakes in a medium bowl. Arrange the salmon fillets in a shallow dish. Pour the marinade over the salmon, turning fillets to coat both sides. Cover, and refrigerate for 20 to 30 minutes.
Meanwhile, make the salmon stuffing by combining the cream cheese, green onions, and 1/2 teaspoon mustard in a small bowl. Refrigerate until ready to cook the salmon.
Preheat oven to 400 degrees F (200 degrees C). Line a baking dish with foil, and lightly grease foil.
Remove salmon from marinade. Cut a slit in the thickest part of each fillet to make a small pocket. Spoon cream cheese mixture into the pocket. Place salmon in prepared baking dish.
Cook salmon in preheated oven for 10 to 15 minutes. Remove from oven; spoon teriyaki sauce over fillets and sprinkle with sesame seeds. Reduce heat to 300 degrees F (150 degrees C). Cook until fish is easily flaked with a fork, about 5 minutes more.