Mix together the soy sauce, Worcestershire sauce, onion powder, garlic salt, thyme, black pepper and chilli powder in a small bowl to form a paste. Spread a thin layer of the soy sauce mixture on both sides of each shark steak. Place on a plate and cover. Allow to marinate in the refrigerator at least 30 minutes.
Preheat oven to 170 degrees C.
Arrange the fish on a baking tray. Bake in the preheated oven until cooked completely through, about 40 minutes, turning the steaks over once, about half-way through the cooking time.