01 - Slice the peeled bananas and add them to a blender along with the Greek yogurt, honey or maple syrup, and vanilla extract. Blend on medium-high until the mixture is completely smooth and creamy, about 30 seconds.
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 gently until smooth.
03 - Pour half of the banana-yogurt mixture into the popsicle molds, filling each cavity about halfway. Drizzle a generous layer of the melted chocolate over the surface.
04 - Using a thin skewer or the tip of a knife, gently drag through the chocolate drizzle in a figure-eight motion to create a marbled effect. Avoid over-mixing to keep distinct swirls.
05 - Divide the remaining banana mixture among the molds, filling them to just below the rim. Drizzle with more melted chocolate and repeat the swirling technique for a layered marbled look throughout.
06 - Place popsicle sticks into the center of each mold. If desired, sprinkle the tops with chopped roasted nuts or mini chocolate chips, pressing gently so they adhere to the surface.
07 - Transfer the molds to the freezer and chill for a minimum of 4 hours, or until the popsicles are completely firm and frozen through.
08 - To release each popsicle, briefly run the outside of the mold under warm running water for 10 to 15 seconds. Gently pull the stick to slide the popsicle free. Serve immediately.