In a bowl, whisk together the soy sauce, barbeque sauce (I used a Chinese one), ginger and coconut milk. Check the taste of the marinade adding more soy sauce, barbecue sauce or ginger to your taste.
Place the chicken, plantain and sweet potato in a large bowl and pour over the marinade. Marinate for 30 minutes.
Gently warm the banana leaf over a fire until the leaf is pliable (do not burn it), just 3 minutes. (Istead of banana leaf and baking sheet, you can use a baking mold with lid, it's not the same but it's better then nothing).
Cut the leaf into four large squares from 30 x 30 cm.
Place the chicken onto the banana leaf square and evenly divide the vegetables on top.
Pour any remaining marinade and fold the leaves around the chicken.
Tie the package and place them in a baking sheet (lined with baking paper).
Bake in a previously pre-heated oven at 180°C until the chicken is tender and completely done (around 1 hour).
Check the package occasionally to make sure they do not burn.