Cook Linguine According To Package Directions. Meanwhile, In A Skillet, Saute The Onions And Garlic In Butter And Oil Until Garlic Is Tender. Sprinkle Chicken With Salt And Pepper; Add To Skillet. Cook For 3 Minutes On Each Side Or Until Lightly Browned. Reduce Heat; Cover And Cook 4 Minutes Longer Or Until Juices Run Clear. Remove Chicken And Keep Warm. Stir The Tomato, Lemon Juice And Parsley Into Skillet; Heat Through. Drain Linguine; Toss With Tomato Mixture. Top With Chicken And Sprinkle With Parmesan Cheese.