Cut beef into 3x1 inch strips; brown in oil in skillet. Transfer to a slow cooker. Combine the next seven ingredients; pour over beef. Cover and cook on low for 5-6 hours or until meat is tender. Add tomatoes and green peppers; cook on low for 1 hour longer. Combine the cold water and cornstarch to make a paste; stir into liquid in slow cooker and cook on high until thickened. Serve over noodles or rice.