01 - Place the sliced bananas, Greek yogurt, honey or maple syrup, and vanilla extract into a blender. Blend on medium speed until the mixture is completely smooth and creamy, scraping down the sides as needed.
02 - Combine the dark chocolate and coconut oil in a microwave-safe bowl. Heat in 20-second intervals, stirring between each, until fully melted and glossy. Alternatively, melt over a double boiler, stirring constantly.
03 - Pour half of the banana mixture into the popsicle molds, filling each about halfway. Drizzle a generous layer of melted chocolate into each mold. Use a skewer or thin knife to gently swirl the chocolate into the banana base for a marbled effect.
04 - Divide the remaining banana mixture among the molds, filling them to the top. Drizzle with more melted chocolate and swirl again to create additional marbling throughout.
05 - Insert a popsicle stick into the center of each mold, pressing gently to seat it. If desired, sprinkle chopped roasted nuts or mini chocolate chips over the exposed surface.
06 - Transfer the filled molds to the freezer and freeze for a minimum of 4 hours, or until the popsicles are completely firm and frozen through.
07 - Briefly run warm water over the outside of each mold for 10 to 15 seconds to loosen. Gently pull the popsicle stick to release. Serve immediately.