The recipe can stand at room temperature, covered, for up to 2 hours before serving.
Heat 3 tablespoons of the oil in a large enameled cast-iron casserole. Lightly flour the fish and season with salt and pepper. Cook over moderate heat until lightly browned and cooked through, about 3 minutes per side, depending on the thickness of the fish. Transfer the fish to a platter.
Add the garlic to the oil and cook over moderate heat until deep golden, about 2 minutes; discard the garlic. Add the escarole to the casserole along with the anchovies, olives and capers. Cook, stirring constantly, until the escarole turns bright green and wilts, about 3 minutes. Transfer the escarole to a bowl.
Heat the remaining 1 tablespoon of oil in the casserole. Add the tomatoes and cook over moderately high heat, stirring, until thickened, about 5 minutes. Add the tomato sauce to the escarole and season with salt and pepper. Garnish with parsley and serve with the fish.