Stir together the soy sauce, honey, 2 tablespoons mustard, ginger, garlic and crushed chillies 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, spring onions and 1/2 teaspoon mustard in a small bowl. Refrigerate until ready to cook the salmon.
Preheat oven to 200 C / Gas 6. 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 150 C / Gas 2. Cook until fish is easily flaked with a fork, about 5 minutes more.