Place the xylitol, slightly melted coconut oil, and eggs into a mixing bowl, then whisk thoroughly until combined.
Add the oat flour, rolled oats, and baking powder, then mix well with a spoon.
Cut the chocolate into small cubes and add half of it to the mixture.
Chop the walnuts into smaller pieces and stir them into the dough.
Line a baking tray with parchment paper and place tablespoon-sized mounds of dough onto it. Leave enough space between them, as they will spread while baking. Flatten them slightly as well – the thinner they are, the crispier the cookies will become.
Sprinkle the remaining chocolate pieces on top.
Bake in a preheated fan oven at 190°C / 374°F for 25-30 minutes.