Step 1: Season chicken thighs with salt, black pepper, allspice, and thyme.
Step 2: Heat oil in a large pot over medium-high heat and brown chicken on both sides, about 5 minutes per side. Remove and set aside.
Step 3: In the same pot, add brown sugar and cook until melted and bubbling, about 2 minutes.
Step 4: Add onion, garlic, bell pepper, and carrots. Cook until softened, about 5 minutes.
Step 5: Stir in soy sauce and ketchup, then return chicken to the pot.
Step 6: Add chicken broth and scotch bonnet pepper (if using). Bring to a boil, then reduce heat to low, cover, and simmer for 30 minutes.
Step 7: Remove chicken and set aside. Stir cornstarch mixture into the gravy and cook until thickened, about 3 minutes.
Step 8: Return chicken to the pot, heat through, and garnish with green onions before serving.