Boil chicken breasts until done. Cut into bite size pieces. Meanwhile chop onion finely. Mix 1 cup cheese with the onion and chicken pieces. Set aside. Mix Ro*Tel, sour cream, and cream of chicken in medium bowl.
Place 1/2 Ro*Tel mixture in bottom of nonstick 13x9 baking pan. place a layer of tortillas over Ro*Tel mixture. Then pour chicken mixture over tortillas, then place another layer of tortillas, top with remaining Ro*Tel mixture. Top with remaining cheese.
Bake at 350 degrees F about 10 minutes or until cheese is hot and bubbly.