Heat oil in large skillet on medium-high heat. Add chicken and onions; cover. Cook 10 to 14 min. or until chicken is done (165ºF), turning after 6 min. Remove chicken from skillet; cover to keep warm.
Add tomatoes, dressing and lemons to onions in skillet; cook 4 min. or until heated through, stirring frequently.
Return chicken to skillet. Spoon sauce over chicken. Cook 1 min. or until chicken is heated through; top with cheese.