Slice the chicken breasts into thin strips about 2" long. Add the cornstarch and chili powder and mix well. Set aside.
Mix together the chicken broth, oyster sauce, sesame oil, and soy sauce. Set aside.
Wash and dry the scallions well. Cut off and discard the root ends, then slice the rest of the stalks into 2" to 3 " pieces. Set aside.
In a wok or skillet over high heat, add the canola oil. Heat oil on high until hot but not smoking. Add the chicken, garlic, and ginger, and stir fry until chicken is no longer pink, about 1 to 2 minutes. Stir to prevent sticking.
Add the chicken broth mixture and cook for another minute or two until almost half of the liquid has evaporated and the remainder forms a thick sauce. Add the scallions and toss together for 20 seconds. Remove from heat and serve over warm rice.