If using dried noodles, soak them according to package directions until pliable, then drain. In a small bowl, whisk together all sauce ingredients: oyster sauce, soy sauce, fish sauce, dark soy sauce, and sugar. Set aside. Ensure all vegetables and chicken are chopped and ready.

Heat 1.5 tbsp of oil in a large wok or skillet over high heat until it shimmers. Add the sliced chicken and stir-fry until it's cooked through and lightly browned. Remove the chicken from the wok and set aside.

Add the remaining 1.5 tbsp of oil to the wok. Add the minced garlic and chopped chilies and stir-fry for about 30 seconds until fragrant. Add the onion, bell pepper, and Chinese broccoli. Stir-fry for 2-3 minutes until the vegetables are tender-crisp.

Add the drained noodles and the cooked chicken back to the wok. Pour the prepared sauce over everything.

Toss everything together quickly and thoroughly for 1-2 minutes, ensuring the noodles are fully coated in the sauce and heated through. Turn off the heat and immediately stir in the fresh holy basil leaves until they are just wilted.

Serve immediately while hot, garnished with a few extra basil leaves if desired.