Mix the yogurt, sour cream, and garlic and allow to rest in the refrigerator over night if possible.
Make a paste of the cornstarch and milk.
Preheat the oven to 375 degrees. Preheat an oiled skillet to the smoke point.
Brush or spray one side of the filet with the remaining olive oil. Coat that side with the seeds. Carefully lay the filet in the hot skillet and sear it to a golden brown crust. Do not turn the fish. Place skillet in the oven and bake for 4 minutes.
While the fish is baking, slowly bring the yogurt mixture to a simmer, stirring continuously. If you are too aggressive the sauce will break. This is not a disaster, but it doesn’t look as good. Add the cornstarch milk and stir in the crawfish tails and cook until the tails are warm.
Plate the fish and cover with the sauce. It will need some salt. Your call as to how much.