Mashed Potatoes and Rutabaga with Lemon

Name: Mashed Potatoes and Rutabaga with Lemon
Ingredients: 2 pounds rutabaga (yellow turnip), peeled and cut into 2- inch pieces; 2 pounds Yukon gold potatoes, peeled and quartered; 12 tablespoons unsalted butter, at room temperature; 1 1/2 cups half-and-half, warmed; Kosher salt; 1 tablespoon extra-virgin olive oil; 1 1/2 tablespoons finely grated lemon zest; 8 scallions, white and green parts, chopped, plus extra, whole, for garnish; 1/3 cup finely chopped fresh parsley; 1 1/2 cups fresh, unseasoned breadcrumbs