Combine the sliced chicken with the water, cornstarch, oil, and oyster sauce. Mix well to combine, and set aside for 15 minutes while you prepare the other ingredients for the dish.
When you’re ready to cook, heat a wok or cast iron/carbon steel skillet until it just starts to smoke.
Add 1 tablespoon oil, and spread it around to coat.
Add the chicken, and stir-fry until the chicken is mostly cooked and lightly browned.
Turn off the heat, remove the chicken to a bowl, and set aside.
Over medium-low heat, add the remaining 1 tablespoon oil to the pan, along with the garlic and ginger, and fry for 1 minute until fragrant.
Increase the heat to medium-high, add the curry paste, and fry for another minute.
Stir in the brown sugar.
Add the onion, bell pepper, green beans, bamboo shoots, and fish sauce, and fry for 2 minutes, until the onions begin to wilt.
Then reduce the heat to medium-high, and add the coconut milk.
Bring to a simmer over medium-high heat. (From this point on, keep the curry at a simmer. Avoid boiling it too high, or the coconut milk may split and have a grainy appearance.)
Stir in the chicken, and simmer for 1 more minute.
Finally, stir in the Thai basil, just until it wilts.
