Cut beef into 1/4-inch-thick strips, about 2-1/2 inches long. Combine with cornstarch, oil, garlic, ginger, salt and pepper in bowl. Chill 30 minutes.
Pare broccoli stalks to remove tough skin. Cut stalks from tops. Cut tops into flowerettes. Slice stalks 1/4-inch-thick. Cook in pot of boiling salted water for 2 minutes; drain; transfer to bowl.
Remove stems from mushrooms. Slice caps 1/4 inch thick.
Cook rice following package directions. When almost cooked, coat large skillet with cooking spray; heat over medium-high. Add mushrooms; sauté 5 minutes, until wilted; add to broccoli. Increase heat to high. Add beef to skillet; stir-fry 2 to 3 minutes. Add broccoli, mushrooms, teriyaki sauce; heat through. Sprinkle with cashews. Serve with rice.