Place the diced apple in a small, microwave-safe bowl. Microwave on high for 90 seconds to 2 minutes, or until the apple pieces are fork-tender.
Whisk together all remaining ingredients in a medium-sized mixing bowl with the cooked apples. Spoon into a jar with a tight-fitting lid.
Close and refrigerate for at least 4 hours, but preferably overnight before eating.
Notes
I like using unsweetened almond milk for our oats, but feel free to use whatever milk you'd like—soy, oat, dairy, coconut—it'll all work!
Leaving the peel on the apple is all about personal preference, so you do you! Some folks like the chewy texture and added nutrition, some folks prefer their apples peeled.