Chicken salad

Ingredients
4 cups diced poached chicken, recipe follows
1 stalk celery, cut into 1/4-inch dice
4 scallions, trimmed and thinly sliced or 1/4 cup sweet onion cut into 1/4-inch dice
1 1/2 teaspoons finely chopped fresh tarragon or fresh dill
2 tablespoons finely chopped parsley
1 cup prepared or homemade mayonnaise
2 teaspoons strained freshly squeezed lemon juice
1 teaspoon Dijon mustard
2 teaspoons kosher salt
Freshly ground black pepper