Preheat oven to 350°F. Prepare the chocolate by chopping it up.
Grease and dust with flour the bottom and sides of a 14-inch rectangular tart pan (with removable bottom) with coconut oil. (This recipe also works in a 9-10 round tart pan or even a traditional pie pan although with a pie pan, you'll have to serve the tart in the pan).
Do not chill the can of coconut milk overnight or it will separate. And to ensure the fat is not separated out, shake the can hard before making the chocolate.
Make The Crust
Use a blender or food processor to combine the crust ingredients. Stop as soon as the mixture resembles a dough. If it is too crumbly, add more of oat milk.
Press the crust mixture evenly into the bottom of the greased pan. Start forming the edges first, and then smooth out the center with a flat-bottomed glass.
Puncture the crust on the bottom in several places with a fork to ensure air bubbles don't form.
Bake for 12 to 18 minutes. Watch it carefully as oven temperatures vary. You want the overall color to be brown, but of course, not burned.When it's ready, remove from oven and sit the pan on a wire rack to cool to room temperature. Do not remove the tart from the pan yet or it will break. If the bottom has bubbled up at all, gentle press flat while it is still warm with the bottom of silver measuring cup or other flat bottle.I set the crust still in the pan into the freezer while I make the filling.
Make The Chocolate Ganache Filling
When the crust is cooled, make the chocolate filling:
Shake the room-temperature can of coconut milk, open it and pour the contents into a sauce pan. Heat the milk on the stove on medium heat until simmering. Don't boil.
Chop the chocolate bars into chunks. Place the chunks in a pile in a mixing bowl, and pour the coconut milk over the top and wait 10 seconds.
With a metal (very dry) spoon, stir the mixture until the chocolate is completely melted and smooth.
Stir in the vanilla extract and salt until combined.
Remove & Fill Tart Crust
When the chocolate filling is ready, it is time to remove the tart crust from the pan in order to fill the tart.Remove the tart by pressing upward on the center (removable) panel, and gently transfer it to a cookie sheet.
Pour the chocolate mixture into the baked yet cooled crust, and smooth the top with a spoon until it is even. Refrigerate for at least 2 hours, or until firm.