Preheat oven to 350 degrees. In a large bowl, combine melted butter, sugar, brown sugar, and salt. Stir in oats and press into a 9x13-inch pan. Bake for 15 minutes. Let cool.
Melt chocolate chips and peanut butter together in a saucepan over low heat, stirring constantly. Spread over baked crust and refrigerate until firm, about 1 hour.