Clean turkey necks with vinegar or lime. Rinse with water, pat dry and place into a bowl. Add jerk seasoning, garlic, salt, and lemon juice. Let marinate for at least 30 minutes.
In a heavy pan, heat oil and add tomato paste. Let tomato paste cook for 1 - 2 minutes. Add turkey necks with marinade and let slow cook on low to medium heat for about 25 to 30 minutes. Add water only when necessary. Continue to cook until meat is tender (15 - 20 minutes).
Let turkey necks continue to roast in the pan while stirring occasionally (almost like pan-frying) for about 5 minutes. Add onion and let cook for another 2 minutes. Remove from heat and serve hot with a side of rice.