Preheat the oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper and set aside.
Cream the butter and light brown sugar in a large bowl with a hand mixer or stand mixer until light and fluffy.
Add the peanut butter and mix until fully incorporated.
Beat in the eggs one at a time, mixing well after each, then add the vanilla and mix until combined.
In a separate bowl, whisk together the all-purpose flour, old-fashioned oats, baking powder, and salt.
Fold the dry ingredients into the wet mixture until just combined, then stir in the chocolate chips.
Press about two-thirds of the dough evenly into the bottom of the prepared pan.
Arrange the halved Snickers bars in a single layer over the dough.
Drop the remaining dough by rounded teaspoons over the Snickers pieces; it does not need to completely cover them.
Bake for 27 to 29 minutes, until the top is golden and set. Remove from the oven and let cool completely in the pan before cutting into 36 bars.