Put the shallots, garlic, and chilies in a food processor and blend until all the ingredients are well-combined. Then, add the olive oil, thyme, orange juice, vinegar, mango, and salt to it. Blend again till it becomes smooth. Place the fish fillet in this mixture and refrigerate it for about 45 minutes. Then, remove the fish, reserving the marinade. Put the marinade into a saucepan and bring it to a boil. Then, reduce the heat and let it simmer for about five minutes.