1. Butter an 8-inch square baking pan with nonstick cooking spray, then line with parchment paper, with overhang on all sides. 2. Process the wafers in a food processor until fine crumbs form. (You should have 1 1/2 cups crumbs.) Add the confectioners' sugar and salt and pulse until well mixed. Add the butter and 3/4 cup peanut butter and pulse, scraping the bowl occasionally, until evenly moistened. 3. Transfer to the prepared pan and spread in an even layer. Arrange the banana slices in a single layer on top and press in firmly. Freeze until set, about 30 minutes. 4. Meanwhile, combine the chocolate chips and remaining 1/4 cup peanut butter in a heatproof bowl. Set over a saucepan of simmering water and melt, stirring occasionally, until smooth. Pour over the banana layer and spread evenly. Sprinkle the peanuts on top and gently press into the chocolate mixture. 5. Freeze until firm, at least 4 hours. Lift out of the pan with the parchment overhang. Cut into 2- by 1-inch bars. Bars can be frozen in an airtight container for up to 1 week.