Mix the oyster sauce, dark soy sauce, light soy sauce, fish sauce, brown sugar, rice vinegar, white pepper, and water in a small bowl until smooth.

Heat a large wok or skillet over high heat until very hot and slightly smoky.

Add vegetable oil and swirl to coat the pan evenly.

Add the sliced chicken and stir-fry until lightly browned with golden edges and fully cooked through.

Toss in the garlic and chilies and cook briefly until fragrant and aromatic.

Add the onion, broccoli, bell pepper, and snap peas and stir-fry until crisp-tender with slight charring on the edges.

Add the drained noodles to the wok and gently toss to combine without breaking the noodles.

Pour the prepared sauce over the noodles and stir continuously until everything is glossy and evenly coated.

Let the noodles sit against the hot pan for a few seconds at a time to develop smoky caramelized spots.

Stir in the Thai basil and green onions until wilted and fragrant.

Serve immediately while the noodles are hot, glossy, and steaming.