Heat oven to 375 degrees F. Coat 12 muffin cups with no-stick cooking spray.
Combine flour, sugar and peanut butter in large bowl with a fork until even crumbs form. Stir in walnuts. Reserve 1 cup for topping.
Add flax seed, baking powder and salt to flour mixture. Stir in milk, bananas and egg until evenly moistened. Stir in dates. Divide evenly in muffin cups using a heaping 1/4 cup batter each.
Sprinkle reserved crumb mixture on top.
Bake 28 to 30 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes before removing from pan.