How to Make It
Cook fregola in a large pot of boiling salted water according to package directions. Rinse, drain, and spread in a single layer on a rimmed baking sheet; let cool 5 minutes.
Preheat a grill pan or cast-iron skillet over medium-high. Toss together onions, oil, ½ teaspoon of the salt, and ¼ teaspoon of the pepper in a medium bowl. Grill or griddle onions, turning occasionally, until lightly charred and white parts are tender, about 6 minutes. Let cool, then coarsely chop.
Stir together butter, shallot, garlic, lemon zest, lemon juice, dill, and remaining ½ teaspoon salt and ¼ teaspoon pepper.
Just before serving, melt butter mixture in a small skillet or microwave. Toss dill butter with cooked fregola and charred onions. Top with a little more dill.
Tip: Pack the fregola, dill butter, and dill garnish separately. Melt the butter at the party and fluff it into the fregola. Then garnish.