Preheat the oven to 350 degrees Fahrenheit and line a muffin tin with muffin papers. As an alternative, you can spray the holes with cooking spray.
Whisk together the wet ingredients in a large bowl until creamy.
I find this is easiest when I first mash the banana until it’s creamy, then stir in the peanut butter until creamy, and then whisk in the milk and eggs.
Add in the dry ingredients (oats, ground cinnamon, sea salt) and mix until well-combined. If adding, stir in the chocolate chips.
Pour the oatmeal mixture into the prepared muffin pan, filling the holes all the way up. Bake on the center rack of the preheated oven for 30 to 40 minutes, or until the baked oatmeal has set up and is golden-brown. Allow the oatmeal muffins to cool for 20 minutes before unwrapping them and eating.
Serve peanut butter banana baked oatmeal muffins with a drizzle of peanut butter or almond butter, a simple powdered sugar glaze, or a dollop of yogurt and fresh fruit if desired. Additional banana slices, blueberries, and a drizzle of pure maple syrup are also great!