In a large bowl, combine soy sauce, olive oil, brown sugar, apple cider vinegar, allspice, thyme, cinnamon, nutmeg, garlic powder, onion powder, cayenne pepper, salt, and pepper. Whisk until well blended.
Add the chicken thighs to the marinade, ensuring they are fully coated. Cover and refrigerate for at least 2 hours, or overnight for best flavor.
Preheat your grill to medium-high heat.
Remove chicken from the marinade and discard the marinade. Grill the chicken for about 6-7 minutes per side, or until the internal temperature reaches 165°F.
While the chicken is grilling, prepare the mango salsa by combining diced mango, red onion, jalapeño, cilantro, lime juice, and salt in a bowl. Mix well and set aside.
Once the chicken is cooked, remove it from the grill and let it rest for 5 minutes before slicing.
Serve the grilled jerk chicken topped with the fresh mango salsa.