Heat oil in a large saute pan. Add leek and garlic; sauté until leek is translucent, about 5 minutes. Add escarole and sauté, stirring constantly, until escarole is limp, about 1 minute; stir in water. Cook over high heat, stirring frequently, until escarole is tender and broth evaporates, about 3 minutes. Add salt and pepper to taste.
Spoon escarole-mixture into a 1 1/2-quart glass baking dish. Sprinkle cheese, bread crumbs and walnuts over top. Bake about 15 minutes. Enjoy.