Preheat the oven to 375 degrees fahrenheit.
In a large mixing bowl mash the bananas.
Whisk in the brown sugar until combined, then whisk in the peanut butter and egg. After thoroughly mixed, whisk in the milk and vanilla.
Stir in the oats, chia seed, baking powder, and salt.
Once mixed, pour into a greased 8x11 baking dish and sprinkle the top with chocolate chips.
Bake for 30-35 minutes until completely set.
Remove from the oven and let cool for about 20 minutes before serving.