Heat canola oil in a wok over medium heat. Add ginger and let it sizzle for 15 seconds. Next, add garlic and dried red pepper. Stir, then pour in sake. After a few seconds, add in sesame oil, soy sauce, mirin, and 2 cups water. Turn heat down to medium low and bring the mixture to a simmer.
In a small bowl, mix together 1 tablespoon of water and cornstarch, until a thick slurry forms.
Slowly add the cornstarch slurry to the sauce while stirring constantly, and simmer for 1-2 minutes until the sauce thickens and coats the back of a spoon. Remove from heat and set aside.
In a large bowl, combine cornstarch, flour, baking powder, salt, ground ginger, sesame seeds, and crushed red pepper and whisk until combined. Pour in water and whisk until a batter is smooth and coats the back of your spoon. If mixture is too thick, add an additional tablespoon of water.
Pour canola oil in a medium-sized, heavy bottom saucepan until it is about 1½ inches thick. Bring oil up to 375 degrees (using a candy thermometer helps make sure the temperature is right).
Once oil is at the right temperature, add cauliflower to batter. Working in batches, use a slotted spoon to transfer the cauliflower from the bowl to the oil, allowing the excess batter to drip off before dropping into oil. Fry cauliflower, rotating with a slotted spoon to make sure all sides are being cooked, until cauliflower is golden brown, about 5-6 minutes. Transfer cauliflower to a paper towel lined plate and continue frying additional batches.
Right before serving, place sauce back on low heat until it is just warm. Transfer cauliflower to sauce and toss to coat. Serve cauliflower over jasmine rice garnished with scallions and sesame seeds.