Remove noodles from package; reserve seasoning packet. Break block of noodles in half. In medium saucepan, bring 2 cups water to a boil. Add noodles; reduce heat and simmer uncovered 3 minutes, stirring occasionally. Remove from heat; drain.
Heat 5-quart nonstick Dutch oven or wok over medium-high heat until hot. Add beef strips and garlic. Stir-fry 3 minutes. Add mushrooms; cook and stir 3 minutes or until mushrooms are tender and beef is no longer pink. Stir in onions. Add spinach in batches, stirring 30 seconds per batch until spinach wilts. Remove from heat; stir in seasoning packet, juice concentrate, 2 tablespoons water and ginger. Add cooked noodles; toss to mix.