1. Sprinkle roast with salt and pepper on all sides. In a large skillet over high heat, heat oil; brown roast on all sides. 2. Place onions in a slow cooker; place roast over onions. 3. In a medium bowl, mix tomato paste, 1/4 cup water, Worcestershire sauce, rosemary, and garlic; pour over roast. 4. Cover and cook on HIGH 6 to 7 hours or on LOW 8 to 10 hours, or until meat is very tender. Remove meat to a platter; cover and keep warm. 5. In a small bowl, whisk remaining water into flour until smooth. Whisk flour mixture into onions and sauce in slow cooker until thickened. Serve onion gravy over roast.