Preheat the waffle iron and set to medium heat.
Cut the taro into 1 to 2-inch thick batons. Then, grate the taro with a food processor or by hand. Transfer the grated taro to a large bowl. (See note 4 about cutting taro by hand)
Add the sliced scallions, cassava flour (or all-purpose flour), soy sauce, oil, mushroom powder, salt, garlic powder, onion powder, sugar, white pepper, and chili flakes to the bowl. Using your hands, mix the ingredients together for 1 to 2 minutes, until the taro mixture is moist. Grab a clump of the taro mixture and give it a squeeze. The taro mixture should hold its shape.
Grease the waffle iron generously with oil. Measure a scant half cup of taro mixture and place it over one of the quadrants of the waffle iron. Using your fingers, flatten the mixture slightly. Prepare 3 more waffles and close the waffle iron with the lid. Cook the waffles for 6 to 8 minutes, until golden brown (see note 5). Transfer the cooked waffles to a cooling rack.
Continue cooking the waffles with the remaining taro mixture. If you want to keep the earlier batches of waffles warm, heat your oven to 225ºF (110ºC). Place the cooling rack with the cooked waffles over a large baking sheet and place the baking sheet and waffles into the oven.
Serve the taro waffles while they’re still warm. Enjoy them on their own or with sweet chili sauce.