Line a baking sheet with parchment. Make sure it fits in your freezer.
Peel and slice bananas into 1/4–1/3-inch rounds.
Aim for even thickness so they freeze and sandwich neatly.
Stir peanut butter with vanilla and maple syrup (if using) until smooth. Taste and adjust sweetness.
Make banana “sandwiches”: Spread a small dollop of the peanut butter mixture on one slice, then cap with another slice. Place on the lined sheet.
Freeze for 20–30 minutes, until the sandwiches are firm and easy to handle.
Melt chocolate with coconut oil in a microwave-safe bowl in 20–30 second bursts, stirring between each, until silky.
Alternatively, melt over a double boiler.
Dip each frozen banana sandwich into the melted chocolate, letting excess drip off. Set back on the parchment.
Before the chocolate sets, sprinkle with flaky sea salt and chopped nuts, if using.
Freeze again for 15–20 minutes, until the chocolate is set. Enjoy straight from the freezer or let sit 2–3 minutes to soften slightly.