The sweet-sour-spicy chili sauce at the center of this dish is built on fish sauce, lime juice, brown sugar, soy, and sambal. It's a Thai-adjacent flavor profile that shows up across Southeast Asia, and the balance of the four main elements (salt, acid, sweet, heat) is what makes the sauce work. Too much of any one and the whole thing tilts out of balance.
Fish sauce is the umami-salt foundation. Lime is the bright acidic counter that keeps the sauce from feeling heavy. Brown sugar provides the sticky caramel sweetness that lets the sauce lacquer onto noodles. Sambal (or sriracha) brings the specific red chili heat that defines Southeast Asian cooking. One to two teaspoons of sambal is enough; the other ingredients mellow it just enough to eat comfortably.
The chicken sears first. Bite-size pieces of thigh, seasoned directly in the pan with salt and pepper, left undisturbed for 3 to 4 minutes to develop fond and golden browning. Flip and cook 1 to 2 more minutes.
Vegetables go in with the chicken still in the pan. Julienned green beans, shredded carrots, green onion whites, all tossed briefly in the chicken fat. Ginger, garlic, and fish sauce for 20 seconds until aromatic. This is the point where the kitchen starts smelling distinctly Southeast Asian.
Rice noodles go in directly with three-quarters of the chicken stock. Press them down so they submerge. The noodles cook in the stock as it reduces, absorbing the aromatic base into every strand. 3 to 4 minutes of simmering, stirring occasionally. If the noodles need more time, splash in the remaining stock. The exact amount varies by pan size, heat, and noodle brand.
The final sauce components (soy, fish sauce, brown sugar, lime, sambal) go in near the end so the lime and sambal stay fresh. Cilantro only at the very end, off the direct flame, to preserve color and flavor.