Line a 9 x 13-inch rimmed quarter sheet pan with parchment, leaving enough overhang on two sides to lift the frozen slab. Clear a level shelf in a freezer set to 0°F or colder so the liquid base will not tilt before it firms. Keep the Greek yogurt refrigerated while organizing the remaining ingredients, and chop the peanuts into small, irregular pieces that will adhere to the chocolate without making the finished bark difficult to break.
Place the cold Greek yogurt, creamy peanut butter, maple syrup, vanilla, and fine salt in a medium bowl. Whisk slowly at first so the thick yogurt stays in the bowl, then whisk firmly for 45 to 60 seconds, scraping the bottom and sides with a silicone spatula. Stop when the mixture is evenly beige, glossy, and completely streak-free. Do not whip in excessive air because large bubbles create brittle pockets and an uneven frozen surface.
Scrape the yogurt mixture onto the center of the prepared pan. Using an offset spatula, spread it into an even layer reaching close to the pan edges, aiming for approximately 1/4 inch thickness throughout. Sweep the spatula lightly across the surface to fill shallow spots, especially near the corners, without repeatedly working the mixture. Place the pan in the freezer for 10 minutes while melting the chocolate; this brief chill helps the drizzle remain distinct instead of sinking into the yogurt.
Combine the semisweet chocolate and refined coconut oil in a dry microwave-safe bowl. Microwave at 50 percent power for 30 seconds, stir thoroughly, then continue in 15-second intervals, stirring after each, until nearly melted. Let the residual heat finish the last small pieces, usually within 60 to 90 seconds total. The chocolate should flow smoothly from a spoon but should not feel hot. Let it stand for 1 minute so it will not melt channels into the chilled yogurt.
Remove the pan from the freezer and drizzle the melted chocolate evenly over the yogurt using a spoon. For a lightly marbled appearance, drag the tip of a skewer through only a few chocolate lines, keeping most of the topping on the surface. Immediately scatter the chopped peanuts over the wet chocolate and press down only loose pieces. Return the uncovered pan to the level freezer shelf and freeze for at least 4 hours, until the center is rigid and no indentation remains when pressed lightly.
Lift the fully frozen slab from the pan using the parchment overhang and place it on a dry cutting board. Peel away the parchment, then break the slab into about 20 irregular pieces by hand; for more controlled portions, press a chef’s knife straight down rather than sawing. Transfer the pieces to a freezer-safe container immediately. Before serving, set out one portion for 3 to 5 minutes, just until the yogurt loses its frosty surface and becomes creamy enough to bite without bending or melting.
