Combine chicken breast, broth and onion in a large pan. Cover, bring to boiling, reduce heat and cook 30 minutes.
Remove chicken, dice and set aside, reserving broth.
Heat butter and grated onion in a large saucepan; stir in zucchini and corn. Cook about 5 minutes.
Just before serving, mix in diced chicken, cream cheese and avocados. Serves 6-8.