Whisk together chia seeds through cocoa powder until smooth. Refrigerate for at least 2 hours. Transfer to a blender and blend until smooth.
Line an 8x8 pan with one sheet of plastic wrap large enough so that the ends can be folded over the top of the pan (smooth out as many wrinkles as possible so they don’t get stuck in between cake layers).
Cover the bottom with one layer of graham cracker sheets, breaking the sheets if necessary to get a flat layer. Spread a thin layer of pudding over the sheets—about ½ to ¾ cup. Repeat layering until pudding is gone, ending with a layer of graham crackers. Freeze for at least two hours.
Once frozen, unmold the cake by gently overturning the pan over a cutting board or serving plate and removing the plastic wrap.
Combine the Greek yogurt with vanilla and maple syrup--consistency will be pourable. I sort of poured most of it on top and let it drape over the sides, using a spatula to spread it around more evenly. Top with fresh cut fruit, sprinkles, shaved chocolate, etc. and freeze for an additional 25-40 minutes, or until yogurt hardens.
Slice and serve!
Store in the freezer (yogurt may get soft in the fridge). Thaw at room temperature for 5-10 minutes before serving.