In a large bowl, combine chicken pieces with chopped onion, garlic, ginger, scallions, stripped thyme leaves, browning sauce, allspice, salt, and pepper. Massage the marinade into the chicken until well-coated. Cover and refrigerate for at least 4 hours, preferably overnight.

Heat vegetable oil in a Dutch oven over medium-high heat. Remove chicken from the marinade, scraping off and reserving the aromatics. Sear the chicken in batches for 3-4 minutes per side until deeply browned. Set the seared chicken aside.

Lower the heat to medium and add the reserved marinade aromatics to the pot. Cook, stirring occasionally, for 2-3 minutes until they begin to soften.

Stir in the sliced carrots and chopped bell pepper. Cook for another 2 minutes. Add the ketchup and soy sauce, stirring to combine. Return the seared chicken to the pot.

Pour in enough water or chicken broth to come halfway up the chicken. Add the whole Scotch bonnet pepper and the remaining sprigs of thyme. Bring to a boil, then reduce heat to low, cover, and simmer for 45-60 minutes, or until the chicken is tender.

Remove the lid for the last 10-15 minutes of cooking to allow the gravy to reduce and thicken. Remove the Scotch bonnet pepper and thyme sprigs before serving. Serve hot with rice and peas.