In a small saucepan, melt 2 tablespoons of the butter over medium-low heat. Add the scallions and a pinch of salt and cook, stirring, until softened, 3 to 4 minutes (don't brown). Take the pan off the heat and stir in the Worcestershire sauce and hot sauce. Cool to room temperature.

In a medium bowl, combine the mayonnaise, 1 tablespoon of the chopped parsley, 1 teaspoon of the lemon juice, the lemon zest, the mustard, 1/4 teaspoon salt, and a few grinds of pepper. Stir in the cooled scallion mixture. Add the crab and mix gently but thoroughly.

In a 10-inch skillet, melt the remaining 1-1/2 tablespoons butter over medium heat. Add the breadcrumbs and cook, stirring, until light golden brown, about 4 minutes. Transfer to a medium bowl and mix in the remaining 1 tablespoon chopped parsley and 1/4 teaspoon salt.

Stuff the shrimp: Line a rimmed baking sheet with parchment and rub lightly with butter. Arrange the butterflied shrimp on the baking sheet. Using a spoon or your hands, mound a heaping tablespoon of the crab mixture onto each shrimp. Sprinkle and pat the breadcrumbs over the crab. (This will be messy; don't worry if there are crumbs on the baking sheet.) Flip the tail of each shrimp up and over the crab.

Bake the shrimp: Position a rack in the center of the oven and heat the oven to 400 degrees F. Bake until the shrimp are cooked through, the crabmeat is hot, and the crumbs are golden brown, 12 to 14 minutes. While the shrimp are in the oven, toss the frisee and the whole parsley leaves with the remaining 1/2 teaspoon lemon juice, the olive oil, and a pinch of salt. On 8 small plates, arrange a small pile of the salad and two shrimp. Serve right away.

Make Ahead Tips: You can butterfly the shrimp, make the stuffing and breadcrumb topping, and stuff the shrimp up to a day ahead. If stuffing ahead, don't top with the crumbs or flip up the tails until ready to bake. Cover and refrigerate the shrimp and stuffing; store the crumbs airtight at room temperature. Remove the stuffed shrimp from the fridge while the oven is heating.