Meanwhile, boil diced potatoes in water until fork-tender. Transfer cooked potatoes to a blender and reserve at least 1 cup of potato water. Add garlic powder, onion powder, turmeric, paprika, cumin, chili powder, salt, pepper, nutritional yeast, oregano, cayenne (if using), and miso to the blender. Start by adding 1/2 cup reserved potato water and blend until all ingredients are incorporated. Taste and adjust salt, cayenne, and water until you get a runny sauce (that's not so thin that it just runs everywhere but not so thick that it's hard to pour). Set aside.