Heat gas or charcoal grill. In large bowl, mix ground beef, soup mix, parsley and steak sauce until well blended. Shape mixture into 8 patties, about 3/4 inch thick.
Place patties on grill. Cover grill; cook over medium heat 13 to 15 minutes, turning once, until meat thermometer inserted in center of patties reads 160°F. Top each burger patty with cheese slice (if desired, cut in half diagonally); cook just until cheese is melted.
Meanwhile, brush onion slices with olive oil. Add to grill last 5 to 8 minutes of cooking time for patties. To toast buns, place cut side down on grill during last 1 to 2 minutes of cooking time.
Layer buns with lettuce, ranch dressing, burger patties, bacon, tomato slices and onion slices.