01 - Arrange three shallow bowls: fill one with the all-purpose flour, whisk together the eggs and milk in the second, and combine the panko breadcrumbs with garlic powder, onion powder, paprika, salt, and pepper in the third.
02 - Pat the cleaned mushrooms thoroughly dry using paper towels to ensure the breading adheres properly.
03 - Working in batches, dredge each mushroom in the flour, shaking off any excess to create a light, even coat.
04 - Dip each flour-coated mushroom into the egg and milk mixture, turning to coat evenly on all sides.
05 - Roll each mushroom in the seasoned panko mixture, pressing gently to help the breadcrumbs adhere firmly to the surface.
06 - Pour the vegetable oil into a deep fryer or large heavy-bottomed pot and heat to 350°F (180°C). Test the temperature with a thermometer for accuracy.
07 - Carefully lower the breaded mushrooms into the hot oil in small batches. Fry for 3 to 4 minutes, turning occasionally, until golden brown and crispy on all sides.
08 - Remove the fried mushrooms with a slotted spoon and transfer to a plate lined with paper towels to drain excess oil. Sprinkle with chopped parsley if desired and serve immediately with your preferred dipping sauce.