Preheat the oven to 350ºF. Spray an 8x8 baking dish with cooking spray and set aside.
In the bowl of an electric mixer fitted with the paddle attachment, mix peanut butter and sugar on high speed until light and fluffy, about 2-3 minutes.
Add vanilla extract and mix until combined.
Add flour, oats, salt, and baking soda and mix on medium speed. The dough will look crumbly.
With the mixer on low speed, add the milk and mix until a dough forms.
Fold in the chocolate chips.
When the dough is completely combined, press evenly into the prepared baking dish. Bake 18-20 minutes or until set and golden on top. Let cool completely before cutting into squares.