Preheat your oven to 180 degrees Celsius (350 degrees Fahrenheit).
In a large mixing bowl, combine the dry ingredients: rolled oats, baking soda, baking powder, chia seeds, cinnamon, and salt. Mix well to ensure the ingredients are evenly distributed.
In a separate bowl, mash the ripe bananas until smooth. Add the flaxseed eggs (or regular eggs), maple syrup, and soy milk. Mix until all the wet ingredients are well combined.
Add the wet mixture to the dry ingredients, as well as the chopped nuts, stirring until everything is well incorporated. The mixture should have a sticky consistency.
Spray a 12-cup muffin tin with cooking oil and line each cup with paper muffin liners for easy removal.
Evenly scoop the oatmeal mixture into each muffin cup. Use the back of a spoon to gently pat down the mixture to ensure it's evenly distributed and compacted.
Bake for approximately 25 to 30 minutes, or until the tops are golden brown.
Allow the oatmeal cups to cool for a few minutes. This will make them easier to remove from the tin without falling apart.
Enjoy the baked banana oatmeal cups immediately, or transfer them to an airtight container and store in the fridge for up to 4 days. You can also freeze them for up to 1 month.