Make the compote by mixing the rhubarb, sugar, vanilla bean and seeds and lemon juice in a small non reactive saucepan. Let it sit for 20 minutes. After the rhubarb has macerated and released its juices, set the saucepan over low heat and cook for about 5-7 minutes, or until the rhubarb is tender. Transfer to a bowl to cool and discard the vanilla bean. Once the rhubarb is cool, stir in the strawberries. You can use the compote immediately, or if you wish, store it in a covered container in the refrigerator until ready to use.
In a medium saucepan, let the tapioca pearls sit in the coconut milk for about 15 minutes. Place the saucepan over low heat and and warm the coconut milk until it is just beginning to simmer. Drop in the vanilla bean and add the sugar. Let the tapioca cook, stirring frequently, taking care to not cook too quickly or let the coconut milk boil. Cook for about 30 minutes, or until the tapioca is translucent and the pudding is thick. Discard the vanilla bean.
Serve the pudding warm or at room temperature with the compote.
Compote lightly adapted from Rhubarb-Strawberry Compote by Pichet Ong, The New Greenmarket Cookbook: Recipes and Tips from Today's Finest Chefs & the Stories Behind the Farms That Inspire Them, by Gabrielle Langholtz (Da Capo Press, 2014).