Method:

1. In a large bowl, combine the chicken legs with the scallions, thyme, vinegar, 1/4 cup lime juice and 1 tablespoon oil. Marinate in the fridge for at least 2 hours or up to 24 hours.
2. If using a grill or grill pan, heat it over high; if using a cast-iron skillet, heat 1 tablespoon of oil over medium-high (If cooking indoors, pat the chicken dry, discarding marinade, then brush the chicken lightly with oil). Season the chicken all over with salt and pepper. Working in batches if necessary, grill or sear the chicken until browned on both sides, 6 or 7 minutes per side. Transfer the chicken to a plate.
3. Meanwhile, in a large pot, heat the remaining 3 tablespoons of oil over medium-high. When the oil is hot, add the onions in an even layer, season with salt and pepper, and let sear without stirring for 3 to 4 minutes. Using a wooden spoon, stir occasionally to prevent onions from burning at the bottom of the pot, and allow onions to cook until they start to caramelize and take on some color, 10 to 12 minutes.
4. Add the bell pepper, chili, garlic, ginger, bay leaves and the mustard (if using), and continue stirring, adding 1 to 2 tablespoons of water as needed to avoid scorching at the bottom of the pot, another 5 minutes. Stir in another 1/4 cup lime juice, and season with 1 tablespoon salt and 2 teaspoons pepper.
5. Add the grilled chicken into the pot, tucking it under the onions, then top with 1 cup of Chicken Stock. Stir well, smooth mixture gently into an even layer, cover and simmer over medium until chicken is cooked through and tender, about 30 minutes.
6. Season to taste and add more lime juice to taste, if desired. Serve chicken over rice, with onion mixture and sauce drizzled generously on top.