Preheat your oven to 350°F (177°C) and prepare a 9" x 13" baking pan with nonstick spray and parchment paper.

Follow the instructions on your brownie mix boxes to prepare the batter, then pour it into the prepared baking pan.

In a stand mixer, beat together the peanut butter and unsalted butter on medium speed until smooth, about 4-5 minutes.

Add the brown sugar, granulated sugar, eggs, and vanilla to the mixture and beat until well incorporated.

In a separate bowl, whisk together the flour, baking soda, kosher salt, oats, and chocolate chips.

Gradually blend the dry ingredients into the wet mixture using a spatula until just combined.

Drop spoonfuls of the oatmeal mixture over the brownie batter, spreading it slightly to let the brownie base peek through.

Sprinkle the Halloween sprinkles and candy eyes on top of the mixture.

Bake the brownies in the oven for 25-30 minutes, checking for doneness with a toothpick.

Allow the brownies to cool in the pan for at least 30 minutes before lifting them out.

While cooling, prepare the frosting by beating together butter, confectioners sugar, vanilla, and cream until creamy.

Add a few drops of green food coloring to the frosting and mix until smooth.

Pipe the green frosting onto the cooled brownies and decorate with candy eyes.

Let the frosting set before slicing the brownies into squares for serving.