Preheat the oven to 350°F.
In a large bowl, combine the mashed bananas, peanut butter, light brown sugar, vanilla, and egg. Stir until well-combined.
Add the almond milk and stir until incorporated.
Add the oatmeal, cinnamon, baking powder, and salt. Stir until well-combined.
Spray a 1½-quart baking dish with cooking spray (I use a dish that measures approximately 9x7 inches); pour the oatmeal mixture into the dish.
Bake for 30 to 35 minutes or until golden brown and set in the middle (a toothpick or knife inserted in the center should come out clean or with a few moist crumbs). The edges will usually have pulled away from the sides of the baking dish as well.
Remove from the oven and let it rest for 10 to 15 minutes. Note: This will allow the baked oatmeal to cool off a bit and firm up so you can cut it into squares, but it will still be warm when served. When the oatmeal is super hot right out of the oven, it will be more loose, and it might fall apart..
Spread the jam evenly over the top of the oatmeal; cut into 6 squares. Best when served warm.
If desired, garnish each piece with extra peanut butter and sliced banana.