Mix chicken with marinade ingredients until coated. For best flavor, let it rest a few hours or overnight—but even 20 minutes works while you prep the noodles.
Boil vermicelli for 3–4 minutes until just tender. Drain and rinse under cold water to keep them from sticking.
Heat a grill pan or skillet until hot. Add chicken and let it sear without moving for charred edges. Flip once, cook through, then rest a few minutes before slicing.
Stir together garlic, lime juice, fish sauce, hot water, and sugar. Add chili if you like it spicy. Adjust to balance sweet, sour, and salty.
Divide noodles into bowls, top with chicken, and drizzle with nuoc cham. Garnish with cucumbers, fresh herbs, and crushed peanuts if you like.
