Peel the potatoes and cut them in half. Boil the potato halves until they are soft (about 20 minutes). Add the kale (or leafy green of choice) halfway through boiling the potatoes and add 10 minutes to the cooking time.
Add liquid margarine (or butter) to a large baking pan and use it to fry the diced unions for about 2 to 3 minutes. Add the vegan bacon to the pan and cook for 5 to 10 minutes.
Drain the kale and potato mix (You can store the liquid to use as vegetable stock later) and add the plant milk and mustard. Use a potato masher to turn the mixture into a smooth puree, adding more plant milk and mustard depending on the smoothness you prefer. Once your desired texture is achieved, add the baking pan contents in and stir until you have a somewhat uniform puree-to-bacon ratio.
(Optional) Leave a little bit of vegan bacon to place on top of the final product for an nice photo finish.