In a mixing bowl, combine finely sliced chicken thighs with fish sauce, brown sugar, grated lemongrass, lime juice, and grated garlic. Toss until all pieces are fully coated in the marinade. Allow the chicken to marinate for 15 minutes at room temperature.

Bring a pot of water to a boil and add the dried vermicelli noodles. Soak the noodles for just 2 minutes until they are tender but still firm, then drain and rinse under cold water. Set aside.

In a small bowl, whisk together natural peanut butter, hoisin sauce, white vinegar, milk, grated garlic, brown sugar, and salt until smooth. Adjust consistency with more milk if needed.

Heat one tablespoon of canola oil in a pan over medium heat. Add the marinated chicken in batches, cook for about 3 minutes or until caramelized and cooked through. Remove from heat.

Fill a large bowl with warm water and dip one rice paper sheet into the water for about 2-3 seconds. Remove and lay it flat on a clean surface.

On each rice paper sheet, layer pieces of the cooked chicken, a handful of cooled vermicelli noodles, finely sliced green and red cabbage, julienned carrot, and fresh coriander and mint leaves. Wrap them tightly.

Gently roll the rice paper away from you, ensuring a snug fit around the filling without tearing. Serve immediately or wrap in cling film in the refrigerator.