Preheat oven to 325.
In a glass, add cocoa mix to 1/4 cup hot water. Stir until dissolved, then set aside.
In a medium mixing bowl, combine all the remaining dry ingredients except for the mini chocolate chips and banana. Mix well and set aside.
Microwave butter in a small dish until melted, then set aside.
In a large mixing bowl, use a fork to lightly beat egg whites for 1 minute. Add melted butter, vanilla, and cocoa mixture, and mix thoroughly.
Slowly stir in the dry ingredients in the wet ingredients in the large bowl. Mix in mashed banana.
Spray an 8 x 8 inch square baking dish with nonstick spray. Pour batter into the dish and top evenly with mini chocolate chips.
Bake in the oven for 30 minutes, or until a toothpick inserted into the center comes out clean.
Let cool slightly, then cut into 9 squares.