Place chicken breasts between plastic wrap and pound with a meat mallet to a 1/2" thickness. Sprinkle both sides of the chicken evenly with salt and pepper.
Heat oil in a large skillet over medium heat. Add chicken; cook 6 minutes on each side or until done. Remove from pan and keep warm.
Add garlic to pan and cook 1 minute, stirring constantly. Add broth and rosemary; bring to a boil while scraping up any browned bits. Cook approximately 3 minutes, until mixture is reduced to 1/2 cup. Remove pan from heat and add wine or lemon juice and butter, stirring until butter melts. Serve sauce over chicken.