Jamaican Rundown

Name: Jamaican Rundown
Ingredients: 1 pound (454g) pickled boneless mackerel (see notes); 1 tablespoon (15ml) coconut oil; 1 large yellow onion (12 ounces; 340g), diced; 2 plum tomatoes (about 4 ounces; 115g each), cored and diced; 2 scallions, ends trimmed and cut into 1/4-inch lengths; 1 medium clove garlic, minced; 3 cups fresh coconut milk or canned coconut milk (about two 13.5 ounce cans (see notes); 1 whole Scotch bonnet pepper; 4 allspice berries; 1 spring fresh thyme; 1 banana boiled green bananas; 1 bunch very green bananas (see notes); Kosher salt; Unsalted butter, softened