Whisk the tapioca starch with 2 Tbsp. of water.
Heat a large saucepan or soup pot over medium heat. Add 1 tablespoon of the coconut oil and brown seitan cubes on all sides. Remove from pan and set aside.
Melt remaining tablespoon of coconut oil over medium-low heat in same pan and add onion and garlic. Cook and stir until soft and translucent, about 10-15 minutes.
Add all remaining ingredients except peas and tapioca starch, and simmer, stirring occasionally, until potatoes and carrots are tender, about 30-40 minutes.
Add reserved seitan and peas and cook 5-10 minutes more. Stir in tapioca starch, remove bay leaf, season to taste and serve.