Peel the bananas and slice each in half crosswise to make 6 pieces total. Stand each piece upright and make a lengthwise slit down the center, stopping about 1/2 inch from the bottom so it opens like a book but stays attached. Spread 2 teaspoons peanut butter inside each banana half, then press in 2 teaspoons chopped peanuts. Gently squeeze closed.

Place stuffed banana halves on a parchment-lined baking sheet, slit side up. Freeze uncovered until completely firm, at least 2 hours or overnight. The bananas should feel solid with no give when squeezed.

In a small microwave-safe bowl, combine chocolate chips and coconut oil. Microwave in 30-second bursts, stirring between each, until smooth and pourable. This takes about 1 to 1.5 minutes total. Let cool 2 minutes so it is not piping hot.

Working quickly with one banana half at a time, use tongs or a fork to dip into the chocolate, turning to coat completely. Let excess drip off for 3 to 4 seconds, then return to the parchment-lined sheet. The chocolate will set almost instantly on the frozen banana.

Immediately sprinkle each coated banana with a pinch of flaky sea salt. Return to the freezer for at least 15 minutes to harden completely. Once firm, transfer to an airtight container with parchment between layers.