- Cut lettuce crosswise into 1-inch strips.
- Cut beef across grain into thin slices. Combine 1 Tbsp. stir-fry sauce and garlic; stir in beef to coat.
- Heat 1 Tbsp. oil in hot wok or large skillet over high heat. Add beef and stir-fry 1 minute; remove.
- Heat remaining oil in same pan. Add onion and ginger; stir-fry 2 minutes. Add lettuce; stir-fry 2 minutes longer. Add beef, tomatoes and remaining stir-fry sauce; cook and stir until vegetables are coated with sauce and tomatoes are just heated through.
- Serve immediately with peanuts.