In a large bowl, combine your chicken pieces with thyme, minced garlic, ginger, soy sauce, and brown sugar. Ensure each piece is well-coated and let the mixture marinate for at least 30 minutes, or up to 48 hours for deeper flavors.

Heat a few tablespoons of vegetable oil in a large pot over medium-high heat until shimmering. Remove the chicken from the marinade, reserving the marinade, and add the pieces to the hot oil. Sear the chicken for about 5-7 minutes until golden brown on all sides.

Lower the temperature to medium and add chopped onions, minced garlic, and grated ginger. Sauté for 3-4 minutes until the onions are translucent. Stir in diced bell pepper and carrots; cook for an additional 3 minutes.

Add the reserved marinade, diced tomatoes, and chicken stock into the pot. Stir well and bring to a vigorous boil, then add the browned chicken back into the pot.

Reduce heat to low, cover the pot, and simmer for about 1 to 1.5 hours. Check occasionally and add water or stock if the liquid level drops too low.

Uncover and let it simmer for another 15 minutes to thicken the gravy. Adjust seasoning if necessary, and serve hot over rice.