Preheat the oven to 350 degrees F (180 degrees C) and line three baking sheets with silicone mats or parchment paper.
Combine All-Purpose Flour (1 1/2 cup), Corn Starch (2 teaspoon), Baking Soda (1 teaspoon), Ground Cinnamon (1 teaspoon), Ground Nutmeg (1/2 teaspoon), Ground Ginger (1/4 teaspoon), and Salt (2 pinch) together in a bowl and whisk them together to aerate them.
Set the dry ingredients aside. Then set up a stand mixer with the paddle attachment. Beat the Banana (1 cup), Unsalted Butter (3/4 cup) and Dark Brown Sugar (1 1/2 cup) together in it thoroughly until it is smooth. Add the Egg (1) and Vanilla Extract (1 teaspoon)
Turn the speed to low and slowly pour in the dry ingredients just until they disappear in. Finally, switch to a spatula and fold in the Old Fashioned Rolled Oats (3 cup) and Chocolate Chips (1 cup).
Use a 1.5-inch cookie scoop to scoop out perfect portions of the cookie dough onto the sheet trays. Bake the cookies for 12-15 minutes, rotating the trays halfway through to ensure even baking.
They should become slightly brown around the edges. Let them cool for 4-5 minutes on the sheet trays, then transfer them to cooling racks to finish cooling. Serve them immediately with a frosty glass of milk!