01 - Place the sliced bananas, Greek yogurt, honey or maple syrup, and vanilla extract into a blender. Blend on high until the mixture is completely smooth and creamy, scraping down the sides as needed.
02 - Combine the chopped dark chocolate and coconut oil in a microwave-safe bowl. Heat in 20-second intervals, stirring between each, until fully melted and smooth. Alternatively, melt over a double boiler set over simmering water, stirring gently until glossy.
03 - Pour half of the banana mixture evenly into 6 popsicle molds, filling each about halfway. Drizzle a generous spoonful of the melted chocolate into each mold over the banana layer.
04 - Using a thin skewer or the tip of a small knife, gently drag through the chocolate drizzle in a figure-eight motion to create a marbled effect. Avoid over-mixing to maintain distinct swirls.
05 - Divide the remaining banana mixture among the molds, filling to just below the rim. Drizzle with more melted chocolate and swirl again if desired. Insert popsicle sticks firmly into the center of each mold. If using, sprinkle chopped nuts or mini chocolate chips over the tops.
06 - Transfer the filled molds to the freezer and freeze for at least 4 hours, or until the popsicles are completely firm and set through.
07 - To release the popsicles, hold each mold under warm running water for 10 to 15 seconds, then gently pull the stick to slide the popsicle free. Serve immediately.