Make It Now:

1. Preheat the oven to 350°F. Spray an 8×8-inch casserole dish with cooking spray.
2. In a medium mixing bowl, add the banana and mashed really well with a fork. Add the milk, eggs, vanilla, oil, and maple syrup and whisk together with the banana until combined. (Another option is that you can throw all these ingredients in the blender and blend until smooth. This will avoid any banana chunks.)
3. In a large mixing bowl, stir together the oats, flax, baking powder, cinnamon, and salt. Pour the wet ingredients into the dry ingredients and stir until well combined. Stir in the blueberries. Pour the batter into the greased casserole dish. (Freezing instructions begin here.)
4. Bake for about 35-40 minutes (if using frozen blueberries or a glass pan, it may take 5-10 minutes longer), or until firm around the edges and the middle is set but not too firm.
5. Make the (Optional) Vanilla Glaze: Let oatmeal cool while you make the Vanilla Glaze. In a small bowl, stir together the milk, vanilla, salt, and powdered sugar. Once the baked oatmeal has cooled a little bit, use the spoon to drizzle it all over the top.
6. Serve the baked oatmeal warm in a bowl with a little milk on top. You can also top with sliced bananas, more blueberries, sliced almonds or chopped pecans, if desired.

Freeze For Later: Skip Step 1. Follow Steps 2 and 3. Tightly wrap the dish in a few layers of plastic wrap or foil (or a tight-fitting lid), fill out and tape on the freezer label, and freeze.

Prepare From Frozen: Thaw completely. Follow Steps 4-6.