Slice the chicken thigh into strips. Add Thai soy sauce, dark soy sauce, sugar, white pepper, and cornstarch. Mix well for about 30 seconds, then add the oil and mix again. This helps keep the chicken juicy.
Prepare the Chinese broccoli by separating the stems from the leaves. Roughly cut the leaves into segments. Cut the stems diagonally into smaller pieces so they cook faster.
Make the sauce by mixing together Thai soy sauce, dark soy sauce, oyster sauce, fish sauce, rice vinegar, and sugar. Stir until the sugar is mostly dissolved.
If using fresh rice noodle rolls, cut them into wide strips and gently unroll each piece. Toss the noodles with a little oil to prevent sticking.
Heat a wok or deep pan over medium heat. Add oil, then add the chicken. Spread the chicken into a single layer and let it sit for 1 to 2 minutes, until lightly browned. Flip and cook the other side. Once the chicken has changed colour and is about 90% cooked, remove it from the wok and set aside.
Add a little more oil if needed. Add the minced garlic and Chinese broccoli stems. Stir-fry for about 2 minutes, until the stems start to soften. Add the Chinese broccoli leaves and cook until just wilted.
Push everything to one side of the wok. Add a little more oil, then crack in the eggs. Gently scramble the eggs, then mix everything together.
Add the rice noodles, then pour in the sauce. Gently toss everything together until the noodles are evenly coated.
Let the noodles sit for about 30 seconds to caramelize and get those charred edges. Flip or toss the noodles, then let them sit for another 30 seconds.
Add the chicken back in and give everything one final toss. Serve hot.