In a large bowl or ziplock bag, combine the chicken, avocado oil, fish sauce, coconut aminos, garlic, ginger, lime zest, coconut sugar, kosher salt, and pepper. Peel off tough, outer layers of the lemongrass stalk (you'll be left with the pale yellow stalk). Now, using a mallet or back of a knife, smash the lemongrass (this helps release it's flavor) and cut it into 1/2 inch chunks. Place in the bowl with the chicken and toss to coat. You can either let it marinate at room temperature for 30 minutes before grilling or cover and let marinate for up to 24 hours.
Meanwhile, combine all of the dressing ingredients in a small bowl and whisk until the coconut sugar is dissolved. Set aside.
In a large bowl, combine the lettuce, carrots, cucumber and green onions. Set aside.
When chicken is ready, heat grill over medium high heat. When hot, brush grill grates with oil. Remove chicken from marinade and shake off excess marinade and remove any of the lemongrass that is stuck to the chicken. Grill chicken until cooked through, about 5 minutes per side.
Remove from grill when cooked through and cover with foil and let rest for 5-10 minutes before slicing.
Slice chicken and set up an assembly line for plating. Allow guests to plate the (undressed) lettuce, the chicken and top with fresh herbs and sliced chiles, then spoon the dressing over the salad.