Begin the sauce before cooking the fish. In a saucepan over medium heat, place all of the sauce ingredients except the cream and butter. Simmer until 1/3 cup liquid remains.
Begin the fish. In a large saute pan over medium to high heat, heat the olive oil. Season the fish with salt and pepper. Add the fish to the hot oil and saute both sides for 3 to 4 minutes, or until golden. Remove the cooked fish steaks when the center bone pulls out easily with tongs, and keep warm.
Meanwhile, add the cream to the sauce and reduce over low heat for 2 minutes. Swirl in the cold butter off of the heat.
Add the tomatoes to the still hot fish pan at the same time and saute for 2 minutes before adding garlic, cilantro, and wine. Cook 1 minute. Add the avocado. Serve by placing the fish on the bed of tomato and avocado. Strain the butter sauce through a fine mesh strainer. Drizzle sauce all around.