
Bring a large pot of salted water to a boil. Prepare an ice bath by filling a large bowl with ice water and keep near the stove. Add the shrimp to the water all at once and cook until they just turn pink and curl into a C shape, about 2 minutes. Immediately transfer the shrimp to the ice bath using a spider or fine mesh strainer. Chill the shrimp fully, then drain and pat dry.
Meanwhile, in a medium bowl, combine the yogurt, pickles, lemon juice, olive oil, mustard, salt, and pepper until smoothly incorporated.
Place the shrimp in a large bowl along with the bell pepper and green onions. Add the dressing, stir gently to combine, then stir in the chives or dill. Serve immediately or cover and refrigerate until ready to serve, up to 1 day.