Combine the onion, brown sugar, soy sauce, red wine vinegar, thyme, oil, garlic, allspice, and habanero pepper (use less of the pepper if you'd like the dish to be less spicy) in a food processor or blender. Blend until smooth. Place the chicken in a bowl, pour about half of the sauce over it, and rub the sauce evenly over the chicken. (Optional: cover and marinate in the fridge for at least an hour.)

Heat a grill pan or skillet over medium-high heat. Add the chicken and cook for 5-6 minutes per side until it’s no longer pink inside.

In a small pan, heat the remaining sauce for a couple of minutes until it slightly thickens. Pour over the chicken when serving.