Lightly grease a 9-inch square pan, or line with parchment paper.

In a large saucepan over medium heat, melt butter. Stir in brown sugar, vanilla and salt. Mix in the oats. Cook and stir over low heat for 2-3 minutes, until ingredients are well combined.

Press half of the oat mixture into the prepared pan. Reserve the rest for topping.

Melt chocolate chips and peanut butter in a small saucepan over low heat, stirring frequently until smooth. Pour the chocolate mixture over the oat layer in the pan and spread evenly.

Sprinkle the remaining oat mixture over the chocolate layer and press in gently. Cover and refrigerate for 2-3 hours or until firm. Cut into bars and serve at room temperature.