Cook rice in water as directed on package.
Meanwhile, in small bowl, combine seasoning mix, broth and soy sauce; blend well. Set aside.
Heat oil in large skillet or wok over medium-high heat until hot. Add garlic and beef strips; cook and stir 2 to 3 minutes or until beef is no longer pink.
Add broccoli and celery; cover and cook 4 to 5 minutes or until crisp-tender, stirring occasionally. Add mushrooms and broth mixture; cook and stir 1 to 2 minutes or until bubbly and thickened. Serve over rice.