Peel the two bananas and add them to a large mixing bowl. Pour in the peanut butter and mash with a fork until no banana lumps remain.
Line a baking sheet with parchment paper, then transfer the banana mixture to the pan. Spread it out in a thin layer. (See photos in this post for reference.)
Melt the chocolate chips in a double boiler. Make one by filling a small saucepan with 1-inch of water. Bring the water to a boil over high heat, then place a heat safe bowl snugly over the top of the pan. Add the chocolate chips and stir often until they melt. Note: If the mixture looks thick, you can add 1 teaspoon of coconut oil to help thin it out.
Drizzle the melted chocolate over the banana layer. Use a fork to swirl the chocolate evenly into the banana mixture. It's okay if they mix a bit! Sprinkle some flaky salt over the top, if desired. Then transfer the pan to a flat shelf in the freezer. Let it freeze for at least 2 hours.
Once the banana layer feels firm, break it into bite-sized chunks. Serve this bark frozen for the best texture; the bananas will melt if left at room temperature. Store the pieces in an airtight container in the freezer for up to 3 months.
Notes
Nutrition information is for 1 piece assuming you break it into 20 evenly sized pieces. Due to the nature of this recipe, each piece might vary. This information is automatically calculated using generic ingredients, so it's just an estimate and not a guarantee.Peanut Butter Note: I tested this recipe with salted, all-natural, creamy peanut butter (the kind you have to stir when you first open the jar). Using a more processed peanut butter might make the mixture thicker. If you use unsalted nut butter, you may want to add a pinch of salt to the banana mixture.