In a medium bowl, combine the sliced chicken breast, 1 teaspoon vegetable oil, 1 teaspoon soy sauce, and 1 teaspoon cornstarch.
Heat your wok over high heat until smoking. Add a couple tablespoons of oil, and then add the chicken to the pan in one layer. Stir-fry the chicken just until it turns opaque, and remove from the wok. Set aside.
Add another tablespoon of oil to the wok, and add the onions. Stir-fry for one minute, then stir in the chicken stock, curry powder, turmeric, sugar, and salt to taste.
Combine the remaining 1 teaspoon of cornstarch with 2 teaspoons of water and mix until the cornstarch is dissolved. Stir it into the curry and stock mixture, and simmer for 1 minute, until thickened. If the sauce isn’t thick enough, add more cornstarch slurry. If it’s too thick, add more chicken stock.
Add the cooked chicken back to the wok, and stir for another 30 seconds. Serve with steamed rice.