Heat a medium pan over medium-high heat. Once hot, melt the butter or add the coconut oil. Add the banana slices and cinnamon to the heated pan and sauté them for 2 to 3 minutes, until the bananas begin to release their natural sugars. Add the maple syrup and stir to combine for one more minute. Add the vanilla, stir, and turn off the heat.
Fill the jars:
Line up 4 overnight oats jars and fill each with ¼ cup of the quick-cooking steel-cut cut oats, ½ teaspoon ground flax (if using), and ½ cup of milk. Using a spoon, and stir to combine.
Divide the bananas foster mixture among the 4 jars and close the lid. You can mix them into the oats or in the morning.
Refrigerate:
Refrigerate the oats for 12 hours (overnight). In the morning, enjoy them cold, straight out of the jar, or warmed in the microwave for 30 seconds to 1 minute. Microwaving them lightly will also soften them up if they did not soak in the liquid long enough or, if they're too tough for your liking.
Notes
Make this recipe in one big bowl or inside 4 individual jars.