In a bowl, combine the shrimp, onions, bell peppers and celery with the beaten egg. Add 1 teaspoon of the Essence, the salt, cayenne, green onions, parsley and baking powder and mix well. Cover and refrigerate for two hours.
Remove the mixture from the refrigerator and form into 6 patties.
In a shallow bowl, combine the cracker meal with the remaining teaspoon Essence. One at a time, dredge the patties on both sides to lightly coat.
In a large, heavy skillet, heat the oil over medium-high heat. Add the shrimp patties in batches and cook on both sides until golden brown, about 8 minutes. Drain on paper towels.
To serve, spread the insides of each toasted bun with tartar sauce, place a patty on the bottom half of the bun, dress with lettuce and tomatoes, and top with the other bun half. Serve hot.
Yield: 6 servings