In large skillet on medium, heat olive oil to medium high. Pat chicken breasts dry and season with salt and pepper. Place in skillet and cook for 4 to 5 minutes on each side, or until outside is nicely browned and lifts easily from pan. Remove chicken from pan, reduce heat to low, and add thyme sprigs and onion. Stir frequently and cook for 3 to 5 minutes until, onions are soft and translucent. Increase heat to medium and deglaze pan by adding lemon juice and scraping up brown bits from pan surface with a wooden spoon. Add chicken broth and continue until bottom of pan is “clean.”