Soak the dried rice noodles in a bowl of warm (not boiling) water for 30 to 40 minutes, until pliable but still slightly firm with a bit of bite. Drain well and set aside. If using fresh noodles, skip the soak and gently loosen the strands so they do not tear.
Toss the sliced chicken with the 1 teaspoon light soy sauce, the cornstarch, and a pinch of the white pepper. Let it sit while you mix the sauce.
Stir together the dark soy sauce, the 1 tablespoon light soy sauce, oyster sauce, fish sauce, sugar, and remaining white pepper until the sugar dissolves.
Heat a large skillet or wok over the highest heat until nearly smoking. Add 1 tablespoon of the oil and lay in the chicken in a single layer. Sear undisturbed for about 1 minute, then stir fry 1 more minute until just cooked through. Move it to a plate.
Add the remaining half tablespoon of oil and the garlic to the pan, then crack in the eggs and scramble them softly for about 20 seconds. Add the gai lan stems and cook 1 minute, then the leaves, and stir fry until bright green and crisp-tender, about 1 minute more.
Add the drained noodles and the sauce, then return the chicken. Toss over high heat, letting the noodles sit against the pan for 10 to 15 seconds between tosses so they pick up a little char, about 2 to 3 minutes total, until the sauce coats everything and the noodles are tender. Serve hot with lime wedges and chili flakes.