In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
Add butter to the bowl of a stand mixer fitted with the paddle attachment. Beat on medium-high speed until smooth, about 1 minutes. Add sugars and beat again until creamed, about 2 minutes. Beat in eggs, peanut butter, and vanilla until just combined.
Pour in the dry ingredients and beat on low speed until just combined. Leaving the mixer on, add in oats and beat until combined. Stir in chocolate chips and Reese's Pieces.
Cover the bowl with plastic wrap and chill in the refrigerator for at least 30 minutes. You can chill the dough for up to 2 days.
Preheat oven to 350˚F. Line two large baking sheets with silicone mat or parchment paper.
Scoop out balls of dough 2 Tbsp at a time, spacing them 2 to 3 inches apart on the baking sheets,
Bake for 12 to 14 minutes until lightly browned on the edges. Remove from oven and press Reese's Pieces into the top for decoration, if desired. Cool on the baking sheet for 5 minutes before removing the cooling racks to cool the rest of the way.