Add the water and cornstarch to a jar or medium bowl.
Use a fork or a small whisk to stir the mixture until the cornstarch dissolves.
Add the soy sauce, hoisin sauce, brown sugar, garlic, ginger, and crushed red pepper (if using).
Stir the stir fry sauce vigorously until well combined. Stir the sauce well right before using too.
Heat the oil in a large, deep skillet over medium-high heat.
Add the ground turkey and salt, break it up some and arrange it in a single layer. Cook for 2 minutes.
Stir the turkey while breaking it up and arrange it in a single layer again. Cook for 2 minutes.
Stir the ground turkey and cook another 2-3 minutes until it is browned, and all the liquid has cooked out. Stir frequently and continue to break up any large pieces.
Add the shredded cabbage mix to the skillet, stir well to combine and cook for 1-2 minutes, stirring frequently.
Lower the heat to medium-low and add the stir fry sauce, stir well to combine.
Cover the skillet and cook the turkey stir fry for 5 minutes to let the flavors come together, stir occasionally.
Add the green onions and stir.
Lower the heat to low, cover and keep warm until ready to serve.