In a small bowl, mix olive oil, salt, mustard, nutmeg and honey thoroughly. Rub this mixture all over the salmon. Place the fish on a baking tray lined with baking paper and bake in a preheated oven at 200 degrees for about 35-40 minutes.
Finely chop the celery stalk. Chop the red onion into white pieces. Cut the mango and avocado into small cubes and place them all together in a deep bowl. Add olive oil, lemon juice, orange juice and grated orange peel and mix. Serve alongside the fish you took out of the oven.