Preheat your oven to 350°F (175°C) and grease a muffin tin or line it with muffin liners.
In a large bowl, combine the rolled oats, baking powder, cinnamon, and salt. Mix well.
In another bowl, mix the mashed bananas, peanut butter, honey (or maple syrup), vanilla extract, and milk until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined. If using, fold in the chocolate chips.
Divide the mixture evenly among the muffin cups, filling each about 3/4 full.
Bake for 20-25 minutes, or until the tops are golden and a toothpick inserted comes out clean.
Allow the oatmeal cups to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.