Make the Vinaigrette: In a bowl or mason jar, whisk together the garlic, chili, brown sugar, lime zest and juice, rice vinegar, fish sauce, and water. Divide mixture in half.
Use half (without oil) for pickling the vegetables. Add the neutral oil to the remaining half to make your salad vinaigrette. Set both aside.
Quick Pickle the Vegetables: Place carrots, cucumber, radish, and optional chili in a bowl or jar. Pour the pickling half of the vinaigrette (no oil) over the veggies and let sit while you prep everything else.
Marinate the Chicken: In a mini food processor, blend lemongrass, garlic, ginger, soy sauce, fish sauce, and oil until mostly smooth. Add the marinade to the chicken thighs and let sit for at least 15–30 minutes or refrigerate up to 24 hours for more flavor.
Grill the Chicken: Heat a grill or grill pan on high. Grill chicken thighs for 4–5 minutes per side until nicely charred and cooked through. Let rest, then slice into thin strips.
Assemble the Salad: Toss cooked rice noodles and salad greens with a little of the vinaigrette to coat. Layer onto plates or a large platter.
Top with grilled chicken, pickled veggies, cherry tomatoes, herbs, and optional boiled egg. Drizzle remaining vinaigrette over the top and serve.