Preheat the oven to 170°C.
Stuffing: Thinly slice the lemongrass, garlic and ginger. Finely chop the red chilli (having removed the seeds and veins if you don't like it too spicy). Mix together in a bowl with the zest and juice of the lime.
Stuff the fish stomach cavities with the mix. Place the fish onto the banana leaf (head to tail on their sides) then wrap them into a parcel and tie loosely with string.
Put onto a tray and bake in the oven for about 25 mins. Unwrap and serve with the vegetables of your choice.