Cut tofu into blocks 1 x 1 x 2 inch pieces. Dredge each piece into tapioca starch until all surfaces are covered thoroughly. Let stand for 10 to 15 minutes.
Deep-fry 3 to 4 minutes at high heat until each piece is about three-quarters of the way done. Remove and drain on a rack or paper toweling. Just before serving, repeat dredging and deep-frying steps, only frying the pieces until golden brown and crispy. Salt lightly.
Slit each piece lengthwise and put Hoisin sauce into each slit to taste. Garnish with coriander or green onions and serve.