Line an 8-inch square baking pan with parchment paper, allowing some to hang over the sides. Set aside

Combine butter, brown sugar, and vanilla in a medium saucepan over low heat until the butter has melted, and the sugar has dissolved

Stir in the oats, cinnamon, and salt and cook for 4-5 minutes, stirring constantly

Transfer half of the oat mixture to the prepared baking pan and press down to create an even layer

In a small microwave safe bowl, melt chocolate chips and peanut butter on high in increments of 30 seconds, stirring between each increment

Pour the chocolate mixture onto the bottom oat layer, leaving a little bit leftover to drizzle at the end. Top with the remaining oat mixture and press down gently. Drizzle the remaining chocolate mixture over top of the bars

Refrigerate for at least 4 hours, or until set. Cut into bars.