1. Mash ripe banana, tomato paste, vinegar, brown sugar, oil, ginger, onion powder, garlic powder, cayenne, salt, allspice, and turmeric together in a saucepan. Add water and stir to combine.

2. Place over medium-high heat and bring to a simmer. Stir to combine. Reduce heat to medium and simmer until reduced and thickened, 7 to 10 minutes. Remove from heat; reserve 3 tablespoons for the basting sauce, leaving about 1/2 cup for the marinade.

3. Transfer ½ cup banana ketchup to a bowl and add lemon-lime soda, soy sauce, garlic, brown sugar, black pepper, and lemon juice for the marinade. Whisk until combined. Add halved chicken thighs and toss to coat.

4. Cover with plastic wrap and marinate in the refrigerator for 4 to 18 hours.

5. When you are ready to cook the chicken, combine reserved 3 tablespoons banana ketchup, soy sauce, brown sugar, oil, and fish sauce in a small bowl for basting sauce.

6. Preheat a charcoal grill until coals are very hot.

7. Remove chicken from the refrigerator and place on metal skewers, folding in half with the smooth side on the outside, the rougher side folded in.

8. Grill chicken over hot coals until no longer pink in the centers, 15 to 20 minutes, turning and basting every 2 to 3 minutes. Serve with accumulated juices or extra basting sauce.