Preheat oven to 180°C (350°F). Line a baking tray with parchment paper.
Peel the apple, remove core and seeds, then finely grate it.
In a mixing bowl, combine rolled oats, grated apple, egg, applesauce, and coconut oil (if using). Stir until a thick, slightly sticky dough forms. If too dry, add water 1 tablespoon at a time.
Scoop small portions of dough and roll into balls or flatten into cookie shapes. Keep them similar in size for even baking.
Place treats on prepared baking tray and bake for 12-15 minutes until firm and lightly browned.
Let treats cool completely on a wire rack before serving.
Store in an airtight container at room temperature for up to 5 days, or refrigerate/freeze for longer storage.