For the coconut chilli chutney, mash the garlic, tomato, red chilli, coconut, turmeric and lime juice in a pestle and mortar until a paste is formed, or blend in a food processor.
Rub the tuna with a little oil, then season with salt and freshly ground black pepper.
Heat a griddle pan until hot, add the tuna and sear on each side for 2-3 minutes.
Remove the tuna from the pan and set aside to rest for a couple of minutes.
For the salad, combine the cabbage and red onion in a medium glass bowl and stir.
In another bowl, make a dressing with the fish sauce, white wine vinegar, palm sugar, coconut milk and lime juice and pour over the salad. Stir then add the herbs and mix until well combined.
To serve place the banana leaf onto a board and pile some cabbage into the centre.
Place the tuna on top then spoon the chutney on top.
Fold the banana leaf over the bottom, then across either side to form a cone like shape, then secure with a cocktail stick. Serve immediately.