Prepare the Chocolate Coating: Set up a double boiler over a gentle simmer, ensuring the water doesn't touch the bowl. Add the 85% dark chocolate and avocado oil to the bowl, stirring occasionally until completely melted and glossy. Remove from heat to cool slightly.
Whip the Yogurt Base: In a mixing bowl, combine the non-fat Greek yogurt, no-salt-added almond butter, maple syrup, and cinnamon. Whisk with a spatula until the mixture is smooth, uniformly colored, and airy.
Assemble the Jars: Divide the yogurt base evenly among the three jars, smoothing the top of each to create a level surface.
Pour the Top: Gently pour the slightly cooled chocolate over the yogurt in each jar, tilting to guide the chocolate into a thin, even layer that covers the entire surface.
Garnish and Set: Immediately sprinkle the wet chocolate with unsalted toasted slivered almonds and cacao nibs, if using.
Flash Chill: Transfer the jars to the freezer for about 15 minutes, or until the chocolate forms a solid, crackable shell. Serve immediately.