1. Preheat oven to 350°. Sprinkle roasts with salt and pepper. Cook 1 roast in 1 1/2 tsp. hot oil in a Dutch oven over medium-high heat 4 minutes on each side. Remove roast; repeat with 1 1/2 tsp. oil and remaining roast. Sauté onion in 1 Tbsp. hot oil in Dutch oven 4 minutes. Add garlic; sauté 1 minute. Return roasts to Dutch oven; add broth, zest, juice, and tomatoes.
2. Bake, covered, at 350° for 3 hours or until beef is tender. Let roasts stand 10 minutes. Slice 1 roast, and serve with 1 1/2 cups tomato mixture. (Reserve remaining roast and tomato mixture for pot roast pies and soup, if desired.)