Trim fat from steak; cut diagonally across grain into thin slices. Heat 1/2 teaspoon oil in a large nonstick skillet over medium-high heat. Add steak and onions; stir-fry 1 minute. Remove steak mixture from pan; keep warm. Heat 1/2 teaspoon oil until hot. Add slaw; stir-fry 30 seconds. Remove slaw from pan; keep warm.
Remove noodles from packages; reserve 1 seasoning packet for another use. Add the water and remaining seasoning packet to pan; bring to a boil. Break noodles in half; add noodles to water mixture. Cook noodles 2 minutes or until most of the liquid is absorbed, stirring frequently. Stir in steak mixture, slaw, and soy sauce; cook until thoroughly heated.