Cream together peanut butter and sugar, then add in the milk and mix well.
On top of that measure the oats, then flour, then without stirring, add the salt, baking powder, baking soda, and cinnamon. Mix those into the flour gently with your finger or a spoon, then mix the whole deal together.
If your dough is too stiff, fold in the chocolate chips, etc. with a wooden spoon. A stand mixer does handle this better than a handheld mixer.
Preheat oven to 350°F and line a couple baking sheets with parchment paper.
Let rest 20 minutes so the oats can soak up moisture and give you a softer cookie that holds together better. You can scoop the dough onto the tray before this rest if you want.
Bake for 12-15 minutes, turning around halfway. You want the edges to just be starting to brown a tiny bit for chewy cookies, more brown if you want crunchier cookies.
Notes
Using a 3 tablespoon scoop to make a nice fat cookie, this makes around 3 dozen cookies.
I much prefer a chewy oatmeal cookie, but these are also good crispy if that's your jam.
You can also use fresh ground wheat, a 1:1 gluten-free blend, or sifted buckwheat flour in place of AP.