Stack beef steaks; cut lengthwise in half, then crosswise into 1-inch wide strips. Toss with garlic. Heat 2 Tbsp. oil in large nonstick skillet over medium-high heat until hot. Add 1/2 of beef; stir-fry 1 minute or until outside surface of beef is no longer pink. (Do not overcook.) Remove. Repeat with remaining beef. Season with salt and pepper. Heat remaining 2 tsp. oil in same skillet over medium-high heat until hot. Add mushrooms; cook and stir 2 minutes or until tender. Remove from heat. Add gravy mix and 1 cup cold water; blend well. Bring to a boil. Reduce heat; simmer 1 minute or until sauce is thickened, stirring frequently. Stir in beef; heat through. Serve over noodles. Pass sour cream. Makes 4 servings.