1. Start by slicing the sausage into bite-sized pieces. Then, chop the cabbage into thin strips and dice the bell peppers and onion. Mince the garlic to round out the aromatic ingredients.

2. In a large skillet or wok heated over medium-high heat, add the sesame oil. Once the oil is hot, add the sausage and cook until browned, about 5 minutes. Next, toss in the onions and garlic, and sauté for an additional 2 minutes, until fragrant.

3. Incorporate the chopped cabbage and bell peppers, and continue to stir-fry the mixture for about 5-7 minutes, or until the vegetables are tender yet still crisp. Pour in the soy sauce and red pepper flakes (if using), and give everything a good mix to ensure the flavors are evenly distributed.

4. Cook for an additional 5 minutes, or until the cabbage is cooked to your desired tenderness. Taste and adjust the seasoning if necessary, adding more soy sauce or a pinch of salt and pepper to suit your preferences.