Wash the mushrooms in cold tap water (2x) and drain. Pile a few on top of each other and gently squeeze as much water as you can. Then place on a plate lined with paper towels to absorb the excess moisture. Repeat with the rest. Cut them in bite-size pieces and set aside.
Combine the breading mix in a large bowl and stir well to combine.
Heat a large frying pan/wok and fill with about 1 ½ inches of oil. Fully coat the mushroom pieces in the breading mix, place in a sieve to shake off excess flour and fry (in batches depending on how big your pan is) on medium-high heat for 3 minutes. Stir gently to turn, lower the heat to medium-low and cook for another 10 minutes. Place on a wire rack while you cook the rest. They will be lightly golden and crispy outside but not super crunchy yet.
For the second frying, increase the heat to medium or medium-high. Fry the mushrooms for 1-2 minutes. Stir continuously for even cooking. Scoop them to the wire rack once golden and very crunchy. Immediately sprinkle with a pinch or two of salt.
Serve with spiced vinegar.