In a medium pot (off-heat) whisk together the powdered sugar, cornstarch, salt and turmeric. Add the coconut milk, and whisk until everything is dissolved (make sure to get into the corners where the dry mixture likes to stick). Slice the vanilla bean in half lengthwise, then use the back of a small knife to scrape out the seeds. Scrape the seeds into the pot and plop in the vanilla pods as well.
Arrange the sliced bananas evenly over the bottom of the pie crust in a single layer (that way they'll be ready once the custard is done).
Put the pot over medium heat and cook, whisking often, until the custard is thickened and reaches a boil, about 5-7 minutes—you should see bubbles in the middle. Remove the pot from the heat and remove the vanilla bean pods.
Pour the custard over top of the bananas in the pie pan (you most likely won’t need it all unless you have a really deep pie pan—save any leftovers in a small bowl for a treat!). Cover the pie with plastic wrap, placing it directly on the surface (this will prevent a skin from forming). Refrigerate for at least 6 hours, or overnight.