- 2 scallions (white and light green parts only)
- 1 rib celery, cut into 2-inch pieces
- 1 pound raw shrimp, peeled and deveined, tails removed
- ½ cup loosely packed fresh Italian parsley leaves
- 1 tablespoon Old Bay® Seasoning
- 1 teaspoon finely grated lemon zest
- ½ teaspoon mustard powder
- ¼ teaspoon ground cayenne pepper
- ¾ cup panko bread crumbs
- Extra-virgin olive oil
- ¼ cup mayonnaise
- 2 tablespoons dill pickle relish
- 2 teaspoons prepared horseradish
- ¾ teaspoon hot pepper sauce
- 4 hamburger buns, split
- 4 leaves romaine lettuce
- 8 very thin slices red onion
- 8 pepperoncini, thinly sliced into rings (optional)
- In a food processor combine the scallions and celery and process until finely chopped. Add the remaining patty ingredients, except the bread crumbs, and pulse briefly until the mixture forms a very chunky mixture, about 8 one-second pulses. There should be many pieces of shrimp remaining, each about the size of a pea. Transfer to a bowl. Add the panko to the shrimp mixture and stir gently until just combined. Form into four patties of equal size, each about 4½ inches in diameter and no more than ½ inch thick.
- Lightly coat a platter with oil. Arrange the patties on the platter, cover with plastic wrap, and refrigerate for at least 30 minutes or up to 2 hours.
- Combine the sauce ingredients. Refrigerate until ready to use.
- Prepare the grill for direct cooking over medium heat (350° to 450°F) and preheat a grill-proof griddle.
- Lightly brush the patties on both sides with oil, place on the griddle, and cook over direct medium heat, with the lid closed, until golden and firm, about 8 minutes, carefully turning once after 5 minutes. During the last 30 seconds to 1 minute of grilling time, toast the buns on the cooking grates, cut side down, over direct heat. Build each burger on a bun with sauce, lettuce, a patty, onion, and pepperoncini, if using. Serve warm.