Preheat the oven to 350°.
Put the olive oil in a skillet over medium heat. Add the ground beef and onion, stirring occasionally, until beef is nicely browned and onions are tender. Drain off any excess drippings.
Transfer the beef and onions to a 3-quart casserole. Stir in the barley, beef broth, oregano, salt, pepper, and tomatoes.
Cover the casserole and bake for 30 minutes. Stir in the frozen vegetables. Cover and bake for about 30 minutes longer, or until the barley is tender.
Serve with crusty rolls or biscuits, along with a tossed salad.
Calories per serving: 312
Fat per serving: 11.7