Preheat oven to 350 degrees. Mix bananas, yogurt, peanut butter, butter, and eggs in a large bowl. Gradually add sugar and brown sugar, untill all is blended.
Mix the flour, flaxseed, baking soda, salt, cinnamon, and allspice in a small bowl. Add flour mixture to banana mixture.
Pour batter into a 9 x 5-inch loaf pan coated with cooking spray. Bake at 350° for 1 hour and 5 minutes or until a wooden pick inserted in center comes out clean. Remove from oven; cool 10 minutes in pan on a wire rack. Remove bread from pan; cool.
For glaze, combine powdered sugar, milk and peanut butter. Drizzle over bread.