Toss the lamb shoulder chunks with the jerk seasoning and salt until evenly coated.
Heat the vegetable oil in a large skillet over medium-high heat. Brown the lamb in batches for 3 to 4 minutes per side, then transfer to the slow cooker.
Add the diced onion, minced garlic, chopped red bell pepper, and beef broth to the slow cooker. Stir to combine.
Cover and cook on low for 7 hours.
Stir in the sliced plantains and cook for 1 more hour on low.
While the stew finishes, pour 1 cup of the coconut milk into a saucepan with 1.5 cups water and bring to a boil. Add the rice, reduce heat to low, cover, and simmer for 18 minutes until tender. Fluff with a fork.
Stir the remaining coconut milk into the finished stew. Serve the stew over the coconut rice and top with chopped scallions.