On a large container of gallon-sized heavy duty zipper top bag combine the shallots, garlic, ginger, lemongrass, brown sugar, fish sauce, lime juice, and chili garlic sauce. Ad the chicken thighs and turn hem to coat well with the marinade. Refrigerate overnight.
Preheat the oven to 425°F. Line a rimmed baking sheet with aluminum foil and spray with nonstick cooking spray. Place the chicken on the baking sheet skin side up and roast for about 45 minutes until the chicken is cooked all the way through, with an internal temperature of 165°F.
Remove from the oven and sprinkle with the peanuts and cilantro if desired (I clearly forgot to do that in these photos. Oops).