Preheat the oven to 350℉/176℃. Line a 9x9 (or 8x8) baking tray with parchment paper and set aside.
In a bowl, add the flour, oats, baking soda, baking powder, cinnamon, cornstarch, and salt. Stir to combine and set aside.
In another large bowl, add the white sugar, brown sugar, oil, and melted butter. Whisk to combine for 1-2 minutes until smooth.
Add in the eggs and vanilla, and continue whisking. Then add in the peanut butter and whisk until smooth, scraping the sides of the bowl as needed.
Add the dry and wet ingredients together gently with a spatula until a soft dough forms. Do not over-mix!
Mix in the chocolate chips a few times until evenly combined - once again, do not over-mix!
Transfer into the prepared pan and spread evenly. Top with extra chocolate chips if desired.
Bake for 40-50 minutes. The bars are ready when a toothpick inserted in the middle comes out clean. Mine took 45 minutes.
