Pre-heat oven to 350 degrees F. In a large bowl, combine together the flour, baking powder, baking soda, cinnamon, and salt.
In a separate bowl, mash the banana. Add the egg, oil, brown and granulated sugars, yogurt, and vanilla and whisk to combine.
Add the banana-egg mixture to the flour mixture and stir until just combined. Fold in the oats, then fold in the chocolate chips.
Line two baking sheets with parchment paper. Take a tablespoon of dough, form a ball and drop the cookie dough ball on the prepared baking sheet. Repeat, spacing the cookie dough balls about 2 inches apart. At this point, I would refrigerate baking sheets with cookie dough balls for about an hour to chill the dough. This will ensure that cookies, when baked, will not flatten out, and that they will remain tall, so that we end up with thick and chewy cookies!
Bake for 12 minutes until cookies are slightly golden brown. Let the oatmeal cookies cool on the baking sheets for 5 minutes, then transfer to wire racks to cool completely.