Coat an 8 1/2-by-4 1/2-inch loaf pan with cooking spray; line with waxed paper, leaving overhang on both long sides. Set aside.
Melt chocolate; cool to room temperature. Meanwhile, in a food processor, puree bananas until smooth.
Stir peanut butter into cooled chocolate until combined, then stir in banana puree. Gently fold in whipped cream until combined. Pour into prepared pan; top with peanuts. Fold waxed paper over top; wrap tightly in plastic. Freeze until firm, at least 3 hours.
To serve: Remove loaf from pan (run a hot towel across sides and bottom of pan, if necessary). Slice about 1/2 inch thick, as needed.
Rewrap remaining (unsliced) loaf, and freeze up to 1 month.