Prepare the Sauce: In a small bowl, stir together the soy sauce, rice vinegar, brown sugar, toasted sesame oil, and optional crushed red pepper flakes until the sugar is mostly dissolved. Set aside. This sauce will add a savory depth and a hint of sweetness to the stir fry, balancing the richness of the sausage.

Brown the Sausage: Heat a 12-inch (30 cm) skillet or wok over medium-high heat. Add the pork sausage and cook for 6 to 8 minutes, breaking it into bite-size pieces as it browns. The sausage should be well browned with no raw pink areas remaining and must reach an internal temperature of 160°F (71°C). Transfer it to a plate with a slotted spoon. This step is crucial for developing flavor and ensuring the sausage is fully cooked.

Adjust the Skillet Fat: Leave about 1 tablespoon of rendered fat in the skillet. If the sausage was very lean and the pan looks dry, add the 1 tablespoon (15 ml) neutral oil. If there is substantially more than 1 tablespoon of fat, carefully spoon out the excess. This will help prevent the dish from becoming greasy while still providing enough fat for cooking the vegetables.

Cook the Onion and Bell Pepper: Add the sliced onion and red bell pepper. Cook over medium-high heat for 3 to 4 minutes, stirring frequently, until the onion begins to soften and the pepper is slightly tender but still brightly colored. This step adds sweetness and color to the dish, enhancing the overall flavor profile.

Add the Aromatics: Stir in the garlic and ginger. Cook for about 30 seconds, just until fragrant. Keep the mixture moving so the garlic does not brown or burn. This will infuse the oil with aromatic flavors that will permeate the entire stir fry.

Stir-Fry the Cabbage: Add the cabbage in two or three additions if necessary, tossing after each addition as it begins to wilt. Cook for 5 to 7 minutes, stirring often. The cabbage should shrink noticeably and become tender around the edges while retaining a slight crunch. If it starts browning too quickly before it softens, reduce the heat to medium. This step is key to achieving the perfect texture in the cabbage.

Return the Sausage and Add the Sauce: Return the browned sausage and any accumulated juices to the skillet. Pour the prepared sauce around the edges of the pan and toss everything together. Cook for another 1 to 2 minutes, until the sauce lightly coats the cabbage and the sausage is hot. This allows the flavors to meld together beautifully.

Finish and Serve: Remove the skillet from the heat. Stir in half of the sliced green onions and scatter the remaining green onions over the top. Serve immediately while the cabbage is still tender-crisp. Enjoy this dish hot for the best flavor and texture.