In a bowl, combine 15 ml (1 tablespoon) of horseradish with the lemon zest, lemon juice, and oil. Add the halibut steaks and coat thoroughly. Season with salt and pepper. Allow to marinate in the refrigerator for about 10 minutes.
Pour the vodka in a saucepan. Line a steamer with three lettuce leaves and place at the bottom of the pan. Top with the halibut steaks. Cover and bring to a boil. Steam for about 10 minutes. Remove the steamer from the pan and keep the fish aside on a warm plate.
Reduce the vodka until only about 45 ml (3 tablespoons) remains. Add the shredded lettuce and the remaining horseradish. Let the lettuce wilt and add the carrots. Cook for 1 minute. Remove from the heat and add the sour cream. Season with salt and pepper.
Serve the halibut with the wilted lettuce with horseradish and vodka. Garnish with tarragon.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.