Step 1Prepare the rice cakes: Place the package of frozen rice cakes in a bowl of water until softened and fully defrosted, 1 to 1 ½ hours at room temperature (the cakes can also be placed in the refrigerator to defrost overnight). Remove the cakes from the package and soak them in a bowl of water until the cakes separate from each other, about 2 minutes. Drain and set aside.
Step 2Meanwhile, in a small bowl, soak the mushrooms in enough water to cover until softened, about 40 minutes. Drain the water and dice the mushrooms. Set aside.
Step 3Bring a small pot of water to a boil and add the Chinese sausage. Boil until the sausage is softened, 4 to 5 minutes. Drain the water, slice the sausages on the bias so they are similar in size to the rice cakes. Set aside.
Step 4In a large nonstick pan with fairly high sides, heat 2 tablespoons of oil over medium-high heat until hot. Add the mushrooms and, stirring frequently, cook until the mushrooms tighten and absorb most of the oil, about 2 minutes.Stir in the celery and onion and cook, stirring, until they begin to soften, about 2 minutes. Add the garlic and the cabbage, along with 2 tablespoons of chicken broth, and cook until the cabbage is softened, about 2 minutes. Remove from the pan and set aside.
Step 5Add the remaining 2 tablespoons of oil to the pan, along with the rice cakes. Heat the cakes over medium-high heat, gently but constantly stirring so they don’t stick to one another. Drizzle 2 tablespoons broth over the cakes as they heat, constantly stirring. Continue adding broth and stirring until the cakes are softened and warm throughout, 8 to 10 minutes. Be careful that the cakes do not stick to each other or the pan; however, a little coloring on the cakes is fine.
Step 6Stir the sausage in with the cakes and cook for about 1 minute to heat through. Stir in the soy sauce, chile, oyster sauce and sesame oil, along with the cabbage mixture, and cook for 2 to 3 minutes to marry the flavors. Add the pepper and salt if desired, along with the green onion, stirring to combine.
Step 7Remove from heat and serve immediately.