In a silicone ice cube tray, add melted dark chocolate (mixed with coconut oil) to the bottom of each square. Then add a banana slice to each square. Top with chopped walnuts, natural peanut butter, crumbled banana choco chip muffin, and another layer of melted dark chocolate. Flakey sea salt is optional but highly recommended. Place in the freezer for at least 4 hours before popping the squares out of their mold and enjoy!