1. Marinate chicken breasts in lemon juice, garlic, parsley and pepper for abo ut 20 minutes; cut into cubes and saute quickly; set aside. 2. Meanwhile boil the rigatoni until tender; drain. 3. In a large casserole dish combine soup, sour cream, mayonnasie, thyme and p epper; stir until smooth. 4. Add cooked chicken, mushrooms, green beans, and about quarter of the fried onio ns; mix well. 5. Add cooked pasta, stir well. 5. Sprinkle top with cheese and remaining onions and bake uncovered at 350 deg rees about 30 minutes or until bubbling.