In a bowl mix peanut butter, honey, rolled oats and flax seeds. Note, the oats can be used raw or if you prefer, you can soak them in water, milk or almond milk overnight or for a few hours ahead of time.
Using a paring knife, remove the core of the apple (or you can use any utensil made specifically for this job). Cut around the center of the apple until you are able to push the core out. Cut the inner circle of the apple wide enough so that you are left with a hole that is roughly 1 inch in diameter.
Stuff the hole with the peanut butter mixture.
Cut the apples cross-wise into rings. Save any extra peanut butter mix for another apple.