Heat 1 teaspoon oil in a large nonstick skillet coated with cooking spray; add the onions. Cook and stir over medium heat for 25-30 mutes or until tender and browned. Stir in 1/2 teaspoon salt, vinegar and sugar. Remove and keep warm.
Combine the pepper, thyme and remaining salt; rub over steaks. In the same skillet cook steaks for 4-7 minutes on each side or until meat reaches desired doneness (for medium-rare, a meat thermometer should read 145 degrees; medium, 160 degrees; well-done, 170 degrees). Serve with onions.