Cook frozen beans according to package directions along with the onion; drain.
Meanwhile, in medium saucepan combine parsley, cornstarch, salt, and pepper; stir in water.
Cook and stir till thickened and bubbly.
Cook and stir 1 to 2 minutes more, Stir in yogurt and drained bean mixture; heat through.
Turn into serving dish; sprinkle with the shredded cheese.