Combine bread crumbs, Parmesan cheese, garlic powder, parsley, and salt in a zip-top bag.
Beat egg in a large bowl. Add mushrooms and toss until well coated. Place one mushroom in the bag, seal, and shake to coat. Repeat with remaining mushrooms.
Heat oil in a deep-fryer or large saucepan to 375 degrees F (190 degrees C).
Deep-fry mushrooms until golden brown, about 5 minutes. Remove to a paper towel lined plate to cool and drain.
Crush garlic cloves into tartar sauce and mix well. Place into a small dish and serve alongside mushrooms for dipping.