Line an 8x8" baking dish with parchment paper, set aside.
Add the butter, brown sugar, and vanilla extract to a saucepan and heat over medium-low heat, stirring until the butter is completely melted
Add oats, cinnamon, and salt. Cook and stir for about 5 minutes
Press about half of the oat mixture into the bottom of the prepared baking dish
Melt chocolate chips and peanut butter in a microwave safe bowl in the microwave in 30 second increments, until the mixture is completely melted. Transfer 1/4 cup to 1/3 cup of the mixture to a piping bag (or ziplock bag with a hole cut in the corner) and pour the remaining chocolate mixture over the oat crust in the baking dish.
Top with the remaining oat mixture, packing down once again.
Drizzle the reserved chocolate mixture over the top and pop it in the fridge for 4 hours before cutting it into squares and serving.