Cut the chicken breasts halves crosswise into ½ inch thick slices.
In a medium bowl, combine the light soy sauce, sherry, cornstarch, ginger, sugar, and red pepper flakes. Add the chicken, tossing to coat.
In a wok, heat 1 Tbsp of oil over medium-high heat until very hot.
Add green onions, carrots, and celery. Cook, stirring frequently, until vegetables are tender-crisp. Using a slotted spoon, transfer vegetables to a bowl.
Increase heat to high and add the remaining 1 Tbsp of vegetable oil to the wok. Heat until very hot. Add chicken sauce mixture, and stir-fry until chicken is no longer pink.
Return vegetables to wok with the chicken. Cook until heated through. Serve with peanuts as a garnish.