In a large mixing bowl, combine all-purpose flour, cornstarch, baking powder, salt, paprika, garlic powder, and onion powder. Whisk the dry ingredients together to ensure an even distribution of flavors.
Mix the Wet Ingredients: In a separate bowl, beat the egg and gradually add the club soda while whisking to create a frothy mixture.
Slowly pour the wet ingredients into the bowl of dry ingredients. Stir until you achieve a smooth, lump-free batter. Let it rest for 5-10 minutes to ensure the coating adheres well to the fish.
Pat the fish fillets dry with paper towels. Lightly season with a pinch of salt to enhance the flavor.
Dip each fillet into the batter, ensuring it's evenly coated on all sides. Allow any excess batter to drip off.
Heat vegetable oil in a deep fryer or large skillet to 375°F (190°C). Gently place the coated fish into the hot oil and fry for 3-5 minutes per side, or until golden brown and crispy.
Remove the fish from the oil using a slotted spoon and place it on a paper towel-lined plate to drain excess oil. Serve hot with your favorite sides, such as fries, coleslaw, or tartar sauce.