Place a heavy, preferably carbon steel sauté pan or wok over high heat until very hot. Have ready a sizzle pan or small tray, and a Chinese clay pot or Dutch oven.
Squeeze about 1 Tbsp canola oil into the pan and then add the mushrooms along with a little salt. Stir-fry, tossing and stirring, for about 2 minutes until the mushrooms are well browned. Transfer the mushrooms to the sizzle pan.
Squeeze about 2 tsp oil into the wok and then add the carrots and scallions with a little salt. Stir-fry for about 20 seconds, and then transfer them to the sizzle pan.
Squeeze a little more than 1 Tbsp oil into the wok. Stir the chicken to evenly distribute the marinade, and then add the chicken to the wok. Wait a few seconds for the bottom of the chicken to sear and release from the pan, and then begin to stir-fry it. Toss and turn the chicken for about 45 seconds, and then add the minced ginger and garlic. Stir-fry for a few seconds longer.
Stir the sauce ingredients to release the oyster sauce from the bottom of the container, then add them to the pan. Bring the sauce to the boil, scraping with a heatproof plastic spatula to deglaze the pan surface. Pour the sauce over the chicken and cover the clay pot.
Place the clay pot over low heat for about 1 minute, then raise the heat to medium. Simmer the chicken for about 5 minutes.
Stir the mushrooms, carrots, and scallions into the chicken, cover, and bring to the boil.
Mix the cold water into the cornstarch to make a slurry, or pourable paste.
Uncover the clay pot, push the solid ingredients aside, and then stir in the cornstarch slurry. The sauce will thicken within a few seconds of boiling.
Evaluate the flavor and, if necessary, add a little salt or more soy sauce. If necessary, thin the sauce with a little water or thicken it with a little more cornstarch.