For this particular recipe, I used a white sweet potato, rather than the orange-fleshed variety, because I think they're slightly less sweet. (Though, I'm guessing either would work if you want to give it a shot. You could also use a Yukon Gold potato, if you prefer.) Cut the sweet potato into chunks, then place them in a small pot fitted with a steam basket, and fill it with an inch of water. Bring the water to a boil, then cover and reduce the heat to low, steaming the potatoes until they are fork-tender. Once they potatoes are very tender, fork-mash them and measure out one cup of mashed potatoes to use for this recipe. (Reserve any extra for a curry sauce or smoothie later.)
In a high-speed blender, combine the cup of mashed sweet potato, water, salt, chili powder, nutritional yeast, and lemon juice and blend until completely smooth. Warm the diced tomatoes in a small saucepan over medium heat, then pour the cheese sauce from the blender into the pan and stir well to combine.
Heat the mixture until your desired serving temperature is reached, then serve warm with your favorite chips or crudites.
Leftover sauce can be stored in a sealed container for up to a week. Reheat over the stove, or in a small crock pot, before serving again.