Beef-barley Stew

• 1 onion (chopped)
• 5/8 barley (uncooked)
• 500 gr mixed vegetables any variety (frozen)
• 475 ml beef broth low sodium
• 450 gr extra beef (lean ground)
• 300 gr tomatoes (canned)
• 1 gr oregano leaves (dried)
• 1 gr salt (optional)
• 1 gr pepper
• 1 package water chestnuts