Coat an 8x8-inch baking dish with cooking spray. Line with parchment, leaving a 2-inch overhang on the 2 long sides.
Combine graham cracker crumbs, oats, sugar, and salt in a large bowl.
Melt butter in a medium saucepan over medium heat, then add chunky peanut butter, smooth peanut butter, and vanilla, whisking until well combined.
Add peanut butter mixture to crumb mixture, stirring until combined.
Transfer to baking dish, and use the bottom of a measuring cup or an offset spatula to firmly press mixture into an even layer. Refrigerate for 30 minutes.
Pour melted semisweet chocolate over chilled mixture and, using an offset spatula, spread into a thin layer that covers the entire surface. Refrigerate until hardened, at least 15 minutes.
Heat remaining smooth peanut butter in a small saucepan until runny.
Drizzle peanut butter over chilled chocolate. Drizzle melted milk chocolate over peanut butter. Refrigerate until hardened, about 15 minutes.
Use parchment to lift out chilled block of bars. Using a sharp knife, cut into 12 squares. Let bars stand at room temperature for 10 minutes before serving.