Roasted Branzino with Green Olive Couscous

Name: Roasted Branzino with Green Olive Couscous
Ingredients: 1/2 stick unsalted butter; 1 ruby red grapefruit, zested and juiced; Extra-virgin olive oil; 4 whole branzino, 1 1/2 pounds each, gutted and scaled; Kosher salt and freshly ground black pepper; Green Olive Couscous, recipe follows; Kosher salt; 1/2 pound green beans, trimmed; 1 cup cold water; 1 cup couscous; 1 tablespoon champagne vinegar; 2 tablespoons extra-virgin olive oil, plus more for drizzling; 1 small ruby red grapefruit, zested and juiced; 1 fennel bulb, sliced paper thin, a few fronds reserved; Freshly ground black pepper; 1/4 cup pine nuts, toasted; 1 cup pitted and chopped green olives