Coat skillet with ghee over high heat until hot. Add onion; cook and stir 4 minutes or until browned. Remove from skillet and set aside.
Add beef; cook 10 to 13 minutes for medium-rare to medium, turning once. Remove from heat and transfer to cutting board; let stand 3 minutes before slicing. Meanwhile, return skillet to high heat until hot, add onion, water and balsamic vinegar. Cook for 30-45 seconds or until most liquid has evaporated. Thinly slice beef on the diagonal and serve with onions over top.