Heat oil in large skillet or wok over medium-high heat until hot. Add pork; cook and stir until browned. Remove pork from skillet; cover to keep warm.
To liquid in skillet, add carrots, celery, 1 cup water, soy sauce, sugar, bouillon, garlic powder and gingerroot; mix well. Reduce heat to medium-low; cover and simmer 4 to 5 minutes or until vegetables are crisp-tender. Stir in cooked pork, bean sprouts, onions and pimientos; cook until thoroughly heated.
In small bowl, combine 1/4 cup water and cornstarch; blend until smooth. Gradually stir into mixture in skillet. Cook and stir over medium-high heat until sauce is bubbly and thickened. Serve over chow mein noodles.