Spray a 2-quart baking dish with cooking spray. Place the egg yolks in a mixing bowl and beat until smooth. Put the egg whites in the bowl of an electric mixer fitted with a whisk attachment.
Combine 2/3 cup sugar, cornstarch, salt, and coconut milk in a saucepan and bring to boil over medium heat, whisking frequently. Once it comes to a boil, continue to cook, stirring, for 1 minute. While whisking, slowly pour about 1/2 cup of the hot coconut milk mixture into the egg yolks. Pour the egg yolk mixture back into the pan with the rest of the coconut milk mixture and cook over medium heat, whisking constantly, until the mixture starts to boil. Remove from the heat and stir in the vanilla. Pour the mixture through a strainer into a clean mixing bowl and let cool.
Spread a small amount of the pudding mixture in the bottom of the prepared baking dish. Top with a layer of vanilla wafers then a layer of sliced bananas. Cover with a third of the pudding mixture. Repeat the layers two more times so that you have three layers total ending with a layer of pudding.
Beat the egg whites with ¼ cup of sugar and the cream of tartar until stiff peaks form. Spread the mixture over the top of the pudding, making sure to bring it all the way to the sides. Bake for 15 – 20 minutes or until the meringue is lightly browned. Let cool, then refrigerate until serving.