Grate the onion. Mince the 2 garlic cloves. Line a rimmed baking sheet with foil and spray with cooking spray.
In a large bowl mix the ground beef, rice, onion, garlic, salt and pepper. Form mixture into 2" meatballs and put on the prepared baking sheet. Spray tops of meatballs with cooking spray.
Broil meatballs, 6 inches from the heat, turning to brown all sides. Remove pan from oven and set aside while preparing the sauce.
For the sauce:
Chop the onion, bell pepper, and tomatoes. Mince the garlic and jalapeno.
Heat the oil in a large skillet over medium high heat. Saute the onion, garlic, bell pepper, and jalapeno for about 3 minutes. Stir in stock, rum, olives, tomatoes, ginger, tomato paste, molasses, and lime juice. Bring to a boil, stirring frequently, then reduce heat to low and simmer for about 10 minutes.
Add meatballs and cilantro to the sauce and bring to a boil Reduce heat, cover, and simmer over low heat for about 15 minutes. Turn meatballs occasionally while simmering.
Combine cornstarch and 1 tablespoon cold water in a small cup, mixing well. Stir into the skillet and simmer for 2 more minutes, until the sauce is slightly thickened.