Preheat the oven to 350 degrees. Spray an 8 x 8 baking dish with cooking spray and set aside.
In a large bowl cream together the butter and sugar.
Add in the egg, vanilla, and salt and mix well.
Mix in the flour until just combined.
Add the mashed banana and mix until just combined.
Fold in the mini chocolate chips.
Pour the batter into the prepared pan. Bake for 30-35 minutes or until the edges have browned and the center is baked through.
Remove from oven and cool completely. Cut into 16 bars and serve.