It helps with the mushiness issue if you don't rush the defrosting. If you plan ahead enough to get the package out of the freezer and into the fridge the night before and just let it thaw gradually it hold together better, IME.
As soon as it's thawed, put a combination of crushed ginger and garlic smeared all over the fish and let it sit there in that for a bit. Take it out onto the counter long enough before you are gong to cook it to let it get to room temp. That way you can just use the minimum cooking time and it won't dry out. I saute the ginger/garlic smeared fish in coconut oil and coconut aminos (tastes like soy sauce but made from coconuts instead).