MAKE THE GINGERSNAP CRUST: Preheat the oven to 350°F. Combine the coconut oil, maple syrup and molasses in a bowl, preferably one with a pour spout. Place the oats, pecans, salt, cinnamon and ground ginger in the bowl of a food processor. Blitz until the oats and pecans have been pulverized. With the motor running, stream in the coconut oil mixture and run the food processor until you have a slightly sticky mixture that you can press together with your fingers.
Press the crust mixture into a 10-inch tart pan with a removable bottom, using your fingers or the base of a smooth glass to evenly spread the crust across the pan and up the side. Bake the crust for 15 minutes. Set aside to cool. Clean out the bowl of the food processor.
Once the crust has cooled, scatter 2 tablespoons of the chopped crystallized ginger over the crust.
MAKE THE GINGER SYRUP: In a small, heavy saucepan over medium-low heat, combine the ginger juice or sliced ginger, sugar and ½ cup water. Bring to a simmer, stirring until the sugar has dissolved. Gently simmer for 30 minutes or until the syrup has thickened. If using fresh ginger slices, strain the syrup through a fine-mesh sieve and reserve the ginger for another use, such as candied ginger. Cool to room temperature, set aside 4 tablespoons to use now and store the rest in a covered container in the fridge.
MAKE THE FILLING: Place the dark chocolate in a medium-size heatproof bowl. In a small saucepan, heat the Ginger Syrup and coconut milk until just simmering. Remove from the heat and pour over the dark chocolate. Wait about a minute and then whisk until the chocolate is completely melted. Add the vanilla extract, fine sea salt and cinnamon, and whisk once more. Pour the chocolate mixture into the crust.
MAKE THE TOPPING: :lace the remaining 2 tablespoons chopped crystallized ginger in the bowl of the food processor. Pulse until just coarsely chopped. Add the pistachios and pulse until chopped and well combined. Sprinkle the mixture over the chocolate filling.
Refrigerate the tart for 6 to 8 hours. Allow it to come to room temperature for 10 to 15 minutes before serving.