Combine the hoisin sauce, sesame oil, green onion and sesame seeds in a small bowl. Cut the remaining orange in half and squeeze the juice from it into the bowl with the other ingredients. Mix well.
Place the salmon fillets on a large plate or baking dish. Place about three orange slices over each fillet (more or less depending on the size of your fillets). Spoon the sauce over the salmon. Cover and place in the fridge for 30 minutes.
Wrap each piece of salmon securely in tin foil, spooning a little sauce over each piece. Cook for about 7 minutes on each side. The salmon is done when it flakes easily with a fork.