Using paper towels, pat-dry the chicken thigh pieces. Place in a medium bowl.
Process lemongrass, garlic, ginger, chili, honey, 1 tablespoon sesame oil, fish sauce, and rice vinegar in a food processor until they are well blended and paste-like.
Toss the chicken with the lemongrass paste. Cover it with stretch film and place it in the fridge. Let it marinade for 15 minutes.
Heat 2 tablespoons of sesame oil in a wok or large pan (you can also use a 10-inch cast iron skillet) over medium heat.
Stir in the soy sauce into the chicken mixture and give it a stir.
Cook the chicken thigh pieces for 4-5 minutes on each side or until browned. (see note)
If it dries and starts sticking to the bottom of the pan, add in some chicken stock. Simmer for a few minutes. Cook, stirring frequently until the chicken stock is reduced.
Add in the cashews and mix until they are coated with the sauce. It will start getting caramelized.
Stir in edamame at the last minute. Cook until warm, 3-4 minutes.
Serve with rice and garnish it with chopped serrano chili (if using), scallions, cilantro, and sesame seeds.