Using a sharp cook’s knife, remove the gill coverings and hard fins from the tilapia — this is a messy job, so it’s worth asking your fishmonger to do it for you. Carefully cut 3 evenly spaced diagonal slashes into either side of the fish – tilapia skin is very thick, so you’ll need a firm, steady hand. Place the prepared fish in a dish.
Mix all the ingredients for the marinade together in a bowl or place in a blender or food processor and blend to a smooth paste. Pour the marinade over the fish, reserving a small amount for basting, and rub into the slashes and inside the cavity of each fish. Cover the dish with clingfilm and leave the fish to marinate in the fridge for at least 1 hour, preferably overnight.
Remove from the fridge a few minutes before you’re ready to cook and preheat the grill to medium-high. Place the fish on a baking tray lined with foil and cook under the grill for 25 minutes (add an extra 3–5 minutes if the fish are particularly large or thick) until nicely browned and cooked through, turning and basting with the reserved marinade halfway through the cooking time.
Serve with Green Kpakpo Shito Salsa or plain boiled rice along with lime wedges for squeezing over.