Slice the chicken into thin strips. Chop the bok choy into bite-sized pieces, slice the bell pepper, julienne the carrot, mince the garlic, and grate the ginger.

In a bowl, whisk together the soy sauce, oyster sauce, hoisin sauce, rice vinegar, sesame oil, and optional red pepper flakes. For a thicker sauce, mix the cornstarch with a little water and stir it in. Set aside.

Heat 1 tablespoon of oil in a large skillet over medium-high heat. Add the sliced chicken and cook for about 4-5 minutes until browned and cooked through. Remove the chicken from the skillet and set it aside.

In the same skillet, add more oil if necessary. Toss in the minced garlic, grated ginger, and sliced bell pepper. Stir-fry for 1-2 minutes until fragrant.

Stir in the bok choy and carrot, cooking for about 3-4 minutes until the bok choy wilts slightly. Return the chicken to the skillet, pour the prepped sauce over the stir-fry, and toss to coat. Cook for an additional 2-3 minutes until heated through. Serve hot over rice or noodles, garnished with sesame seeds and green onions.