Marinate chicken: In a bowl, combine sliced chicken with 1 tbsp light soy sauce, 1 tbsp oyster sauce, 1 tsp dark soy sauce, 1 tsp sugar, and 0.5 tsp white pepper. Mix well and let marinate for at least 30 minutes, or up to 2 hours in the refrigerator.

Prepare sauce: In a small bowl, whisk together 2 tbsp light soy sauce, 1 tbsp dark soy sauce, 1 tbsp oyster sauce, 1 tbsp sugar, 1 tsp white vinegar (if using), and 2 tbsp water or chicken broth. Set aside.

Cook eggs: Heat 1 tablespoon of vegetable oil in a large wok or pan over medium-high heat. Pour in beaten eggs and scramble until just cooked through. Remove from wok and set aside.

Stir-fry chicken and garlic: Add another 1 tablespoon of vegetable oil to the hot wok. Add minced garlic and stir-fry for 15 seconds until fragrant. Add marinated chicken and stir-fry until cooked through and lightly browned, about 3-4 minutes. Remove chicken and set aside with the eggs.

Stir-fry noodles and vegetables: Add the remaining 1 tablespoon of vegetable oil to the wok. Add the separated wide rice noodles and stir-fry for 1-2 minutes until heated and slightly charred. Add the Chinese broccoli and continue to stir-fry for 2-3 minutes until tender-crisp.

Combine and finish: Return the cooked chicken and scrambled eggs to the wok with the noodles and broccoli. Pour the prepared stir-fry sauce over everything. Toss vigorously for 1-2 minutes, ensuring all ingredients are evenly coated and the noodles absorb the sauce. Serve immediately.