Preheat oven to 475 degrees. BUTTER WELL two large baking sheets.
Blend together (in blender or food processor) one banana, milk, half the chopped nuts, vanilla, and cinnamon or allspice until well mixed. Pour into large, shallow dish.
Dip bread slices into mixture until well absorbed on both sides. Arrange on well-buttered baking sheets. Bake until golden, turning over once.
Remove from baking sheets. Slice diagonally and dust with powdered sugar. Top with remaining banana and chopped nuts.
This recipe can be altered for different flavors. Substitute one 8 ounce can crushed pineapple for the bananas, using half in batter and the remaining half on top. Use 1/2 cup shredded coconut for the macadamia nuts, also reserving half for topping.