Fill a deep black iron skillet no more than halfway with good, clean oil and heat to 350 degrees. Place the tempura and panko in separate bowls. Season the tempura aggressively with the pepper and Tony Chachere's Seasoning. Toss the shrimp or oysters a few at a time in the tempura and set aside. Let them sit until their natural moisture has soaked through the powder coating, but if you are in a rush you can spritz them with water. When they are gummy, toss them in the panko until well coated.
Please read this carefully: Fry a few shrimp or oysters at a time so that when added to the oil the temperature does not nosedive, and do not overcook. Shrimp and oysters are done to perfection in sixty to one hundred seconds. Every second they are cooked past their prime causes deterioration. Remove from oil and drain on paper towels or on a brown paper sack taken apart and made to lay flat.
Quick Dipping Sauce
Place into a food processor 1 cup of mayonnaise, the juice of a lemon and a 1/4 cup of cilantro. Blend until smooth and serve cold. Always serve with wedges of fresh cut lemon.