Preheat oven to 350°F. with rack in middle. If using chuck, cut across grain into 4 pieces. Pat beef dry and season with 1 teaspoon salt and 1/2 teaspoon pepper. Heat oil in a 4- to 6-quart heavy pot over medium-high heat until it shimmers. Brown beef on all sides, 6 to 10 minutes total. Transfer to a plate with tongs. Add onions, carrots, 3/4 teaspoon salt, and 1/2 teaspoon pepper to pot and cook, stirring occasionally, until vegetables are softened, 8 to 10 minutes. Add wine and zest and bring to a boil. Add beef and return to a boil. Cover pot and braise in oven until meat is very tender, 2 to 4 hours (beef cheeks take longer than chuck). Season with salt and pepper. Serve beef with carrots and sauce.