Grease a 2 quart or 8-inch square pan with butter or coconut oil.
Add the peeled bananas to the prepared baking dish and mash until broken down and smooth. Add 1½ cups milk, ¼ cup maple syrup, 1 teaspoon ground cinnamon, 1 pinch kosher salt, 1 teaspoon baking powder, 1½ tablespoons melted coconut oil or butter, 1 large egg, and 1 teaspoon vanilla extract and mix well to combine.
Add in 2 cups rolled oats and stir just until incorporated and the oats are coated.
Preheat the oven to 350℉ (175℃) and let the oatmeal sit at room temperature while the oven preheats. This will give the oats time to soften and absorb the milk.
Bake for 25-30 minutes, until oats are tender and moisture has been absorbed.
Serve warm or at room temperature with additional maple syrup and chopped walnuts if desired.
Notes
Oats: Use old-fashioned or quick-cooking oats for the best texture. Do NOT use steel-cut oats. Be sure to use certified gluten-free oats for a gluten-free baked oatmeal recipe.Egg-Free: Simply omit the egg, keeping in mind your oatmeal won't set up into a cake-like consistency, but will still be delicious. Dairy-Free: Use your favorite non-dairy milk and coconut oil. Oil/Butter Free: Use any variety of nut butter in place of coconut oil/melted butter. Note on Sweetness: Feel free to use honey in place of the maple syrup, and you can increase the amount of sweetener added by up to an additional ¼ cup if you like really sweet oatmeal. Optional Additions: Feel free to add up to 2 tablespoons each of nut butter, protein powder, and/or ground flax seed. And/or up to ½ cup of chocolate chips or chopped walnuts to the batter if desired. Storage: Store leftover baked oatmeal in an airtight container in the fridge for up to 5 days. To freeze, slice, wrap in parchment, and place in a freezer bag. Reheat slices in a microwave-safe bowl in 30-second intervals, adding milk to loosen if needed.