Preheat oven to 350˚ and cover a baking tray with parchment paper.
Combine butter and peanut butter in a sauce pan skillet and heat over low heat until butter has melted and mixed with the peanut butter. Transfer to a bowl and add in the maple syrup and make sure the mixture is slightly cooled. Add the egg and vanilla extract.
Stir in the flour, baking powder, salt, and baking soda. Stir in the oats and chocolate chunks. Scoop the dough into balls roughly 2 to 3 tablespoons (dough will be a bit sticky). Place on the sheet tray and press down with the palm of your hand until the cookies are flat. Bake for 12 to 15 minutes, until cookies are lightly browning. Remove and let cool on the tray for 5 minutes then transfer to a rack to finish cooling. Cookies will firm up as they cool.