Begin by washing the cabbage thoroughly and chopping it into bite-sized pieces. Set aside.
Heat the vegetable oil in a wok or large skillet over medium-high heat.
Add the sliced onion and sauté for about 2 minutes until it becomes translucent.
Stir in the minced garlic and grated ginger, cooking for an additional minute until fragrant.
Add the sliced bell pepper and julienned carrots to the pan, stirring frequently for about 3-4 minutes until the vegetables begin to soften.
Introduce the chopped cabbage to the skillet, mixing well. Cook for about 5 minutes, stirring often until the cabbage wilts.
Pour in the soy sauce and sesame oil, then season with salt, black pepper, and crushed red pepper flakes (if using). Stir everything together, ensuring the cabbage is well coated.
Continue to cook for another 2-3 minutes until the cabbage is tender but still slightly crisp.
Taste and adjust seasoning if necessary. Remove from heat.
Serve hot, garnished with sesame seeds and chopped green onions if desired.