Preheat oven to 375°.
Lightly spoon flours into dry measuring cups, and level with a knife. Combine flours, cocoa, baking powder, and salt in a large bowl.
Combine sugar, tofu, soy milk, and butter in a food processor or blender, and process until smooth. Add to flour mixture, stirring just until moist. Stir in 2/3 cup marshmallows and 1/4 cup walnuts.
Spread the batter into a 9-inch square baking pan coated with cooking spray. Sprinkle with the remaining marshmallows and walnuts. Bake at 375° for 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack 5 minutes. Cut into squares.
Note: Soy flour and soy milk are often available in health-food stores and some supermarkets.