Heat a gas grill to medium high. In a small bowl, whisk the hoisin sauce, rice vinegar, and soy sauce. In a larger bowl, season the chicken with 1 tsp. salt and 2 Tbs. of the hoisin mixture. Arrange the lettuce leaves, basil, and mint separately on a platter and put the scallions, peanuts, and jalapeño slices (if using) in small serving bowls.
Grill the chicken thighs, covered, until well browned and beginning to blacken around the edges, about 5 minutes (rotate the chicken 90 degrees halfway through cooking each side for the most even cooking). Flip and continue to grill until cooked through, about 5 minutes more per side. Let the chicken rest for 8 to 10 minutes and then chop into 1/4- to 1/2-inch dice. Transfer the chopped chicken to a serving bowl, add the remaining hoisin mixture, and toss to coat thoroughly. Put the bowl on the table with a serving spoon, along with the platter of lettuce and herbs and the condiments. To eat, spoon the chicken onto the middle of a lettuce leaf, top with basil, mint, scallions, peanuts, and jalapeño (if using), and roll the edges of the lettuce leaves up and around the filling and garnishes.
For an interesting hors d’oeuvre, spoon the chicken into very small lettuce leaves, garnish, and set on a platter.