Place the all-purpose flour in one bowl, add 1 teaspoon of salt, black pepper, and whisk to combine. Gradually pour ¾ cup of water and whisk until well combined and smooth.
Combine shredded coconut, panko, and 1 teaspoon of salt in the second bowl and stir to combine.
Working with one piece of mushroom at a time, dredge in the flour mixture, fish it with a fork and slightly shake off any excess. Then dip it in the coconut mixture to coat evenly. Fish it out using a second fork and transfer the breaded mushroom to a baking sheet. Work all the mushroom pieces and spread them out onto the lined baking sheet. Take it to the fridge for 15 minutes.