Preheat the oven to 355°F (180°C).
In a bowl, beat the sugar and milk until it dissolves. Add peanut butter, vanilla and incorporate very well.
Add the oats, oat flour, baking soda, salt and mix using a spatula. Do not over-mix, just make sure there are no flour lumps.
Fold in half of the chocolate chunks to the batter.
Scoop the dough on a non-stick baking sheet or a silicone mat / parchment paper. Make sure to leave enough space between the cookies because they will expand a bit; press them lightly. Distribute the rest of the chocolate pieces on top of the cookies.
Bake for 20-22 minutes. If you want the cookies to be crunchier, let them sit inside the oven (off) for 10-13 more minutes.
Remove the tray from the oven and allow to cool completely before removing the cookies. It is important to allow them to reach room temperature so that they harden.
Store them in an airtight container in a cool place or in the fridge.