Cut beef into 3-in. x 1-in. strips; brown in oil in a 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.