To prep for the icebox cake recipe, mix the Greek yogurt, sweetener, and cocoa powder until it becomes a chocolate mousse-like consistency. Make sure there are no lumps.
Mix the banana pudding mix and the milk until smooth.
To assemble: In the bottom of an 8 x 8 square baking dish, add a couple of spoonfuls of chocolate yogurt (just enough for the crackers to soak up).
Layer 1: Place 4 cracker sheets, pressing them into the pudding. There will be some extra space in between. (Try to alternate which sides have gaps on the following graham cracker layers).
Layer 2: Spoon and spread about 1/3 of the banana pudding mixture. Press the sliced banana pieces of 1 banana into the pudding, then cover with one-third more pudding.
Layer 3: Place 4 more Graham cracker sheets on top, Followed by the remaining third of the banana pudding.
Layer 4: Spread out the 2nd banana’s slices, then fill the gaps between the bananas with about half of the chocolate yogurt. Put the last four Graham crackers down.
Layer 6 (Top Layer): spread the remaining chocolate yogurt on top, smoothing it out or creating a design with grooves. Cover and refrigerate the Graham cracker icebox cake for at least three hours or overnight before enjoying it. You can insert a knife to check if it's done, which should easily go through the graham crackers.