- 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.