Preheat the oven to 320° and grease a square (8 x 8" or 9 x 9") baking dish.
Mash up the bananas with a fork or a potato masher in a bowl.
Add oats, baking powder, cinnamon, milk, eggs, and vanilla extract and mix everything up.
Add the blueberries and gently mix them in as well
Pour the mixture into the baking dish and bake the oatmeal for about 30 minutes, or until the top is golden brown and the oatmeal has set.
Serve warm from the oven. You can drizzle some honey or maple syrup on for additional sweetness.
Notes
Add 1/4 cup chopped walnuts or pecans if you like.
The bananas give this oatmeal the sweetness. If you don't have bananas, you can make this recipe without, maybe add 1/4 cup of sweetener (brown sugar, honey or maple syrup)