In 4-quart saucepan, heat 3 quarts of salted water to boiling over high heat. Add orzo; heat to boiling and cook 4 minutes. Add green beans and cook until orzo and beans are tender, about 4 minutes longer. Drain well.
Meanwhile, from lemons, grate 1 teaspoon peel and squeeze 1/4 cup juice. In large bowl, with wire whisk, mix oil, oregano, 3/4 teaspoon salt, pepper, and lemon peel and juice until blended.
Add warm orzo and beans to dressing in bowl and toss well. Gently stir in tomatoes and cheese.
Each serving: About 340 calories, 12g protein, 44g carbohydrate, 14 total fat (6g sat.), 26mg cholesterol, 1,010mg sodium.