To prepare sauce, stir together orange juice concentrate, soy sauce, water, cornstarch, and garlic powder; set aside.
Use bottle opener or ice pick to make 4 to 5 lengthwise cuts down each carrot (be careful not to cut through carrot). Cut crosswise into 1/4-inch thick slices, forming flowers.
Spray nonstick wok or large skillet with cooking spray. Add carrots to wok. Stir-fry over high heat 1 minute. Add broccoli and cauliflower to wok. Stir-fry 2 to 3 minutes or until vegetables are crisp-tender. Remove vegetables from wok or skillet; set aside.
Add oil to wok. Stir-fry chicken in hot oil 2 to 3 minutes or until no longer pink. Push chicken to sides of wok. Add sauce mixture; cook and stir until boiling. Return all vegetables to wok; cook and stir until mixture is heated through. Serve with hot cooked rice.