Line an 8- or 9-inch square baking pan with parchment paper, waxed paper, or foil. Spray with cooking spray.
Combine the chocolate chips and sweetened condensed milk in a medium saucepan and cook, stirring, over low heat until the chocolate has melted, and the mixture is smooth, about 6 minutes. Pour mixture into prepared pan and spread to even out the surface. Dollop spoonfuls of the SunButter all over the surface and, using a skewer or knife, swirl the SunButter into the chocolate. Top with the chips and pretzels. Cover pan and refrigerate for 1 hour or until firm.
Lift the parchment out of the pan, drizzle with chocolate sauce, and cut into small squares.