Sprinkle roast with salt and pepper. Cook roast in hot oil in a Dutch oven over medium-high heat until browned on all sides. Combine tomato sauce and next 9 ingredients; pour over roast. Add onion, and bring to a boil. Cover, reduce heat, and simmer 3 1/2 to 4 hours or until roast is tender.
Transfer roast to a serving platter, reserving liquid in pan. Combine flour and water, stirring until smooth; stir into liquid in pan. Cook over medium heat, stirring constantly, until thickened and bubbly. Spoon 1 cup sauce over roast, and serve remaining sauce with roast.