Melt coconut oil in a stock pot over medium high heat. Add cumin, shallot, garlic and ginger and cook until beginning to toast, about 30 seconds, then add grated sweet potato. Cook the sweet potato stirring often until it begins to soften, about 5 minutes. Add vegetable stock and peanut butter (and red pepper flakes, if using) and bring to a simmer. Cook for 15 minutes, or until the sweet potato has fully softened and is beginning to disintegrate.