3 to 4 tablespoons butter or coconut oil
2 cups diced onions
1 bay leaf
1 large carrot, diced or julienned
2 celery stalks, chopped
3 cups sliced mushrooms (12 oz)
1 teaspoon dried tarragon
1/2 teaspoon salt
1/4 cup dry white or red wine
¼ cup fresh lemon juice
½ cup vegetable stock or water, heated
1 tablespoon tomato paste
½ cup chopped fresh parsley
3 pounds fish fillet  

Sauté the onions and bay leaf in the butter or oil until the onions are translucent. Add the carrots and celery and continue to sauté for a few minutes before adding the mushrooms, tarragon, and salt. Stir in the wine and lemon juice. Bring to a boil, cover, and simmer on low heat until the vegetables are just tender.

Combine the heated stock or water and the tomato paste and add to the vegetables. Add the chopped parsley.

Place the fish fillets in an oiled baking pan. Spread the sauce on the fillets pieces. The sauce will be thick, but the fish juices will thin it as it bakes. Bake covered at 350˚ for 20 to 30 minutes, until the fish is tender.

pdf of recipe can be found here