Soak walnuts in 3 tablespoons apple juice concentrate. Sift baking powder and cocoa into bowl with flour and make a well. Measure 1 1/3 cups apple juice concentrate, oil, egg white and banana into measuring cup and add all at once to dry ingredients and mix.
Spread in 13 x 9 inch pan sprayed with nonstick spray. Sprinkle with walnuts on batter evenly and smooth nuts into batter with back of spoon. Bake at 350 degrees for 30 minutes. Cover when slightly warm. Cut in 24 servings and store in freezer to keep fresh. Yield 24 brownies.