Step 1Pour the oil to a depth of 3 inches into a deep, heavy skillet and heat to 365 degrees.
Step 2Combine three-fourths cup flour, the egg, milk, one-fourth cup oil, the salt and pepper into a bowl and whisk until lump-free. Add the club soda and mix the batter well.
Step 3Place the remaining one-half cup flour on a plate. Dredge the zucchini slices lightly in the flour, dusting off excess, and then in the batter (letting the excess drip off).
Step 4Fry until crisp and golden brown on both sides, turning once, about 1 1/2 minutes. Drain on paper towels and serve hot with lime or lemon to squeeze over.