Preheat oven to 350°F. In a small bowl combine flaxseed meal with 6 Tbsp. water; let stand 5 minutes. Place dates in another bowl; add boiling water to cover. Let stand 5 minutes; drain. Line an 8-inch square baking pan with foil.
In a blender or food processor combine flaxseed mixture, drained dates, mashed banana, milk, peanut butter, and vanilla. Cover and blend until smooth.
In a large bowl combine the next five ingredients (through salt). Add blended date mixture; stir together just until moistened. Spoon into the prepared pan, spreading evenly.
Bake about 25 minutes or until puffed and set. Cool on a wire rack at least 30 minutes.
Using a fine-mesh sieve, dust brownies with powdered sugar. Cut into 16 brownies. Thinly slice bananas. Fan slices over the tops of brownies. Serve immediately.