Make sure the thin sliced sirloin steaks are no more than 1/4 inch thick. Place the steaks between 2 sheets of plastic wrap and pound very thin. Place steaks on a container and add salt, crushed garlic, lime juice and sliced onion. Marinade for 1 hr.
In a frying pan heat 1 tb. oil and 1 tb. butter. Take steak out of marinade and onion mixture (do not discard this mixture). Brown steak for a few minutes on each side (since they are so thin they will cook quickly). Keep adding oil and butter as needed between steaks.
Once steaks are cooked place on serving platter (keep warm). Add any leftover marinade and sliced onions. If needed add a pat more butter. Sprinkle a little salt over onions and cook until onions begin to caramelize. Pour over steaks. Serve with lime wedges.