Preheat oven to 350 F. In an 8 x 8 inch baking dish, combine first 5 ingredients. Add milk, margarine & walnuts; combine. Spread batter evenly in dish (batter will be stiff). Sprinkle brown sugar & 1/2 cup cocoa over batter.
Pour boiling water over all & bake for about 40 minutes or until batter rises to the top & is baked through.