1. Preheat oven to 380 degrees F (190 degrees C)
2. Arrange onions in the bottom of a medium baking dish.
3. Wash cod fillets and pat dry with paper towels. Season with salt, pepper and garlic powder on all sides.
4. Place fish on top of the onion slices.
5. Sprinkle with thyme and pour the evaporated milk over it. (Milk should almost cover the fish).
6. Cover with foil and bake in the preheated oven for 35 minutes.
7. Remove from the oven, gently take out your fish and pour the liquid into a small saucepan. Mix together flour and wine, until smooth. Add to the reserved liquid and cook for about 3 minutes, or until the sauce thickens. Season with salt and pepper to taste, sprinkle with dill.
8. Serve cod over rice and vegetables, pour some sauce over it.