Grease the bottom of a baking dish with half of the olive oil. Arrange the spinach to cover the entire bottom. Arrange the fish on top. Pour the fish or vegetable broth over the fish and spinach. Sprinkle with salt and pepper. Sprinkle the chopped pimientoes and carrot over the fish, followed by the onion and garlic and, finally, the tarragon. Pour the remaining olive oil over the fish and vegetables.