In a medium-large mixing bowl, add in panko breadcrumbs and set aside.
In a medium sized bowl, mix together flour, cornstarch, salt and black pepper. Slowly whisk in water, making sure that it is not clumpy.
In batches of three to four, drop in hen of the woods mushrooms into slurry then promptly into breadcrumbs. Toss mushrooms in panko until the mushrooms are completely coated. Remove the mushrooms from bowl and set out on a baking tray, making sure not to stack them up.
Bring four cups of canola oil up to 350°f in a two-quart pot (you may need more oil if you are using a larger pot, but just make sure that there is at least three inches of oil in your pot) and drop in mushrooms.