Make the stir fry sauce: Add the water and cornstarch to a jar or a medium bowl. Use a fork or a small whisk to stir the mixture until the cornstarch dissolves. Then add the soy sauce, hoisin sauce, brown sugar, garlic, ginger powder, and crushed red pepper (if using). Reserve the sauce for later. Store it in the refrigerator if not using right away. Stir well just before using.
Heat 2 tablespoons of oil in a large, deep, non-stick skillet or wok over medium-high heat. When the oil is hot and slides around the skillet easily, add the green beans and sprinkle with ¼ teaspoon of salt. Cook the green beans until they are crisp-tender, about 3 – 4 minutes. Stir and toss them often to prevent the beans having direct contact with the bottom of the skillet from burning.
Remove the green beans from the skillet to a bowl.
Heat 1-2 tablespoons of oil in the same skillet or wok over medium-high heat. (If there is still some oil left from the green beans use only one tablespoon of oil, if not use two.)
Add the chicken and sprinkle with ¼ teaspoon of salt.
Arrange it in a single layer and cook for 1 – 1½ minutes until browned on the bottom.
Turn each piece and cook another 1 – 1½ minutes until browned on both sides.
Continue to cook the chicken pieces for 2-3 minutes until cooked through, stir almost constantly. Cut one of the larger pieces in half to make sure it is opaque all the way through and no longer pink in the middle.
Next, add the green beans and the reserved stir fry sauce to the skillet. Stir well to coat the ingredients.
Lower the heat to medium-low and cook for 1-2 minutes until everything is coated and the sauce thickens. Stir frequently.
Taste and add salt, if needed. As a reference we did not add extra to ours.
Serve the chicken and green beans with white rice, noodles or on its own. Garnish with a pinch of chopped cilantro, sesame seeds, or extra crushed red pepper if desired.