Marinate Chicken: In a mixing bowl, combine the sliced boneless chicken thighs with fish sauce, brown sugar, lime juice, grated garlic, and finely grated lemongrass. Stir well and let it sit for about 15 minutes.

Prepare Noodles: Bring a pot of water to a boil and add the vermicelli noodles. Allow them to soak for 2 minutes, then drain and rinse with cold water.

Make Peanut Sauce: In a small bowl, whisk together natural peanut butter, hoisin sauce, white vinegar, and milk until smooth. Adjust consistency as needed, and add chili paste for heat.

Cook Chicken: Heat a non-stick pan over medium-high heat, add canola oil, and cook the marinated chicken until caramelized and cooked through, about 3 minutes.

Soak Rice Paper: Fill a shallow bowl with warm water. Dip each rice paper sheet for 2 to 3 seconds until it is pliable.

Assemble Rolls: On each rice paper sheet, layer a small amount of cooked chicken, vermicelli noodles, finely sliced cabbage, julienned carrots, chopped coriander, and mint leaves. Roll tightly as you go.

Serve: Arrange the fresh rolls on a serving platter and cut them in half if desired. Serve alongside the peanut dipping sauce.