1. Slice the onion and bell pepper, julienne the carrot, mince the garlic, chop the green cabbage, and dice the chicken breast into uniform, bite-size pieces.

2. Melt butter in a large skillet or wok over medium-high heat. Add diced chicken and sauté for 5 to 7 minutes, turning occasionally, until the pieces are evenly browned and cooked through. Transfer the chicken to a separate bowl and set aside.

3. Add onion and garlic to the same pan. Stir-fry for 1 to 2 minutes until fragrant. Add chopped cabbage, sliced bell pepper, and julienned carrot, then cook for about 5 minutes until vegetables are crisp-tender.

4. Return reserved chicken to the pan. Pour in soy sauce, oyster sauce, toasted sesame oil, ground black pepper, and red pepper flakes. Stir thoroughly to evenly coat the ingredients.

5. For a thicker sauce, add the cornstarch-water mixture and cook for 1 minute until the sauce thickens. Serve hot, accompanied by steamed rice or noodles if desired.