I start by preheating my oven to 375°F and lightly spraying an 8×8 inch baking dish with cooking spray. This step matters because a well-greased dish keeps the oatmeal from sticking once it's baked and cooled.
In a large bowl, I stir together the rolled oats, baking powder, cinnamon and salt. Whisking these together first helps the baking powder distribute evenly, so you don't end up with random dense spots in the finished bake.
Next, I pour in the milk, maple syrup, egg (or flaxseed), melted coconut oil, vanilla and sliced bananas. I stir everything together until the mixture looks fully combined and slightly thick, almost like a loose batter.
I add about a cup of chopped pecans into the batter and stir gently to combine. Saving the remaining pecans for the topping gives the finished oatmeal a nice crunchy top layer once it bakes.
I carefully pour the mixture into my prepared baking dish, scatter the rest of the pecans across the top, and bake for 35 to 40 minutes. I know it's done when the top turns golden and a toothpick comes out clean from the center.
Once out of the oven, I let it cool for about 10 minutes before slicing it into 6 portions. From here, I either serve it right away or divide it into meal prep containers for the week ahead.