Mix together the salt, onion powder, pepper, garlic powder, flour and nutritional yeast in a deep bowl.
In a separate bowl, dilute the mustard with the water.
Add 75 g (1/3 cup) of the flour mixture to the mustard mixture and stir. Add the baking powder to the dry flour mixture and mix.
Dip chunks of the mock chicken into the mustard batter, then drop each chunk into the flour mixture and coat with the desired amount of “crust”.
Fry the chunks in hot oil on a medium-high heat in a large skillet or deep fryer until crispy and golden brown, turning as needed.