In a medium bowl, stir together the oats, sugar, cornstarch, cinnamon, baking powder and salt. Then stir in the milk, mashed banana and melted coconut oil until well combined.
Refrigerate overnight, or at least 8 hours.
When ready to bake, pre-heat your oven to 350 degrees. Line a standard muffin tin with liners and fill until almost full.
Bake 25-35 minutes, until tops feel done. Do not over bake. Cool slightly before eating. Depending on the muffin liners you use, they could stick to it if they are too warm, right out of the oven.
Store leftovers in a closed container or zip lock bag in the refrigerator.Note: These taste best right after baking, but if eating as leftovers from the refrigerator, a quick pop in the microwave for 20 seconds is almost as good!