Preheat the oven to 350°F. Line a baking sheet with parchment paper or a silicone mat.
If you need to cook the chicken, boil it in water until done (internal temperature is 165°F). Place the cooked chicken on a plate and allow it to cool to room temperature.
Cut the chicken into small pieces and place them, the oat flour, and egg in a food processor. Process until a dough forms. Transfer the dough to a bowl.
Peel, core, and chop the apple into very small pieces. Add the chopped apple to the bowl and stir it into the dough.
Place the dough on parchment paper. Roll out the dough and use a cookie cutter to cut out the treats. Gather scraps, re-roll until all the dough is used. Place the cutouts on the lined baking sheet.
Bake for 12-15 minutes. Remove from the oven and allow to cool completely on the baking sheet.
Store in an airtight container in the fridge.