Place 18 muffin cups liners in muffin cups; coat liners with cooking spray.
Lightly spoon flours into dry measuring cups, and level with a knife. Combine flours and next 5 ingredients (through salt) in a large bowl; stir with a whisk. Make a well in center of mixture. Combine yogurt, banana, and egg; add to flour mixture, stirring just until moist. Fold in dates, walnuts, and pineapple. Spoon batter into prepared muffin cups. Sprinkle evenly with flaxseed. Bake at 350° for 20 minutes or until muffins spring back when touched lightly in center. Remove muffins from pans immediately; cool on a wire rack.