Fill a large skillet with high sides halfway with oil. Heat over medium-high heat until oil reaches 375° F on a deep fry thermometer.

Meanwhile, Place flour in a shallow dish, salt and pepper to taste. Place egg, mustard and 1/2 tsp. Lemon pepper seasoning in a shallow dish. Whisk until well combined. Place potato flakes and remaining 2 1/2 tsps. Lemon pepper seasonings in a third shallow dish.

Pat fish dry with clean paper towels. Dust with flour, dip in egg mixture and coat with potato flakes, Carefully place in oil and fry until golden brown and fish is cooked through, turning occasionally ( about 3-4 minutes).

Remove from oil with a slotted spoon and drain on paper towels. Keep warm while frying remaining fillets. Serve with lemon wedges and tartar sauce.