Bring 3 cups of water to a boil in a 2-quart or larger pan.
Add the rice, reduce heat and cook, covered, until tender, about 17 minutes.
While the rice cooks, heat the oil in an extra-deep 12-inch skillet over medium heat.
Cut the celery into 1/4-inch dice and add it to the skillet.
Raise the heat to medium-high.
Cook, stirring from time to time, for 2 minutes.
While the celery is cooking, pour the frozen peas and carrots into a colander and spray them with lukewarm tap water for about 30 seconds to begin to defrost.
Set aside to drain.
Add the frozen onions to the skillet.
Stir and cook 30 seconds.
Reduce the heat to medium.
Add the milk and cream of chicken soup and stir to mix well.
Stir in the reserved peas and carrots.
Stir in the Worcestershire sauce, garlic powder, onion powder and black pepper.
Drain the chicken and add it to the skillet.
Stir to break up any large chicken pieces and mix well.
Reduce the heat to low, cover, and simmer until the rice is cooked.
Serve at once over a bed of hot rice.