Heat a large skillet over medium heat. Add 1 pound ground turkey sausage and cook, breaking it into pieces with a spatula and stirring often, until no pink remains and the sausage is cooked through (about 6–8 minutes).
Drain excess fat from the skillet (discard fat or reserve as desired), then return the skillet to medium heat.
Add 1 tablespoon sesame oil to the skillet and swirl to coat the bottom. Add 4 cups shredded green cabbage, 1 cup shredded carrot, 1 cup shredded red cabbage, 1/2 cup thinly sliced yellow onion, 4 cloves minced garlic, and 1 tablespoon minced fresh ginger. Stir to combine.
Add 1 tablespoon soy sauce, 1/2 teaspoon kosher salt, and 1/2 teaspoon ground black pepper to the skillet; stir again to distribute seasonings.
Cook the mixture, stirring occasionally, for 3–4 minutes, until the cabbage has softened but still has a little crunch.
Remove the skillet from the heat and sprinkle with 1/4 cup chopped green onion and 1/4 cup chopped fresh cilantro (if using) before serving.