Grapefruit and Feta Fregola Salad

Name: Grapefruit and Feta Fregola Salad
Ingredients: 8 ounces uncooked toasted fregola pasta or Israeli couscous (about 1¼ cups); 1 small red onion, thinly sliced (about 1 cup), divided; 4 ½ tablespoons extra-virgin olive oil, divided; 1 ¾ teaspoons kosher salt, divided; 2 medium-size red grapefruits (about 8 oz. each); 2 tablespoons fresh lemon juice (from 1 lemon); 1 teaspoon honey; 1 teaspoon Dijon mustard; ½ teaspoon black pepper; 3 tablespoons chopped fresh dill, divided; 2 ½ ounces feta cheese, crumbled (about ⅔ cup); ⅓ cup toasted hazelnuts, chopped