Preheat oven to 350 degrees. Mix the cookie/graham crumbs in a small bowl until the mixture forms a paste. Press paste evenly into the bottom (not up the sides) of 6 individual or 1 large tart pan. Bake the tart crust(s) for 15 minutes or until golden. Remove and allow to cool on wire rack.
Heat whipping cream in a small saucepan over medium heat, stirring frequently to avoid burning. When the cream just begins to boil, remove from heat and add chocolate. Stir vigorously until chocolate is melted and ganache is smooth. Add vanilla, stirring to combine. Allow ganache to cool at room temperature, while you prepare the bananas.
Prepare the topping by slicing 2 bananas in half lengthwise and cutting the halves into 1-inch pieces. Melt the butter over medium high heat in a small pan. When butter is melted, add brown sugar and stir until small bubbles start to form. Add the bananas and allow to cook (be sure to add the bananas right away or the sugar will start to burn), without touching them, for about 40 seconds (they should brown on the bottom). When caramelized, flip bananas over and caramelize the other side for 40 seconds. Remove bananas from the pan when done and place on a plate to use for topping tarts.
Pour a 1/4 inch ganache over the crust in cooled tart pans. Peel the uncooked banana and cut 1/4 inch slices of banana over the top of the first ganache layer. Arrange banana slices so that they do not overlap, but fully cover the ganache layer. Pour the remaining ganache over the bananas. Top with caramelized banana slices. Refrigerate tarts until ganache is fully set, about 1 hour. Tarts may be kept in the refrigerator overnight or served immediately after ganache sets.