Soak 6-8 wooden skewers if you feel like doing skewers. Just grilling the chicken works too.
Combine the garlic, ginger, gochugaru, sesame oil, fish sauce, gochujang and rice vinegar. Stir to combine. Add enough water to make a smooth, fairly thin marinade. 2 tablespoons or so should do it. You are looking for the texture of heavy (whipping) cream. It's not super critical so don't worry too much about getting the "perfect" texture.
If using skewers, cut each chicken into 2-3 pieces. Otherwise leave the thighs whole.
Combine the chicken with marinade. Refrigerate for 1-4 hours.
Light your grill. You want a direct and indirect zone with medium hot heat.
If using skewers thread your chicken onto the skewers.
Place the chicken (or skewers) over indirect heat. Grill, with the lid down until the chicken is almost done. This should take around 12-15 minutes depending on the temperature of your grill.
Move the chicken over direct heat a couple skewers (or pieces) at a time. You are looking for a little char. You don't want to let it burn so pay attention. Once all the chicken is nicely coloured remove it. Check internal temperature. Thighs should read 175F.
To serve as lettuce wraps place a leaf of lettuce on your plate. Top with a bit of rice vermicelli. Place a few small pieces of chicken overtop. Garnish with your choice of toppings. Drizzle a little nuoc cham over the whole thing. Pick it up and enjoy. Might be a little messy but that's part of the fun.