Begin by preheating your oven to 350 degrees and spraying your cookie sheets with non-stick spray.
In a large mixing bowl combine flour, cinnamon, nutmeg, vanilla, sugar, and the mashed banana.
Add in the oil, egg, baking soda, and baking powder and then mix with a hand mixer for about three minutes.
Bake at 350 degrees for 8 to 10 minutes. Edges will be golden brown.
For the filling
Combine the marshmallow creme, vanilla extract, powdered sugar, and slightly softened butter (do not completely melt the butter) in a mixing bowl.
Mix well on a low setting and then beat on high for about three minutes until the mixture becomes fluffy. Use a tablespoon to spread the mixture on the bottom of half of the cooled cookies and then press them together.
Refrigerate for about 20 to 30 minutes before serving. Store any left over cookies in the refrigerator for up to three days