Heat the olive oil in a large enameled cast-iron casserole. Add the shallots and cook over low heat until softened, about 5 minutes. Add the garlic and cook until fragrant, about 3 minutes. Add the escarole and currants and cook over moderate heat, stirring, for 2 minutes. Add the wild rice and cook until warmed through. Stir in the lemon juice and zest and season with salt and pepper. Serve hot.