Trim the monkfish tail back so a little of the bone sticks out at one end and press the flesh down slightly.
Place the chillies, garlic, lime zest and juice, coriander and olive oil into a bowl with a little salt and freshly ground black pepper. Add the monkfish tails and toss to coat then place in the fridge for at least 1-2 hours. Remove the fish from the fridge and return to room temperature before cooking.
Preheat the oven to 200C/400F/Gas 6. Heat an ovenproof frying pan until hot, add the monkfish tails, sear on each side then transfer to the oven and roast for 4-6 minutes until just cooked through. Remove the pan from the oven and let the fish rest for five minutes, turning the fish over once.
Meanwhile, make the pea guacamole. Blend all the ingredients for the guacamole in a food processor to make a coarse purée. Season with salt and freshly ground black pepper then spoon into a serving bowl and top with the olive oil.
For the salsa, place all the ingredients into a bowl and mix gently to combine. Season with salt and freshly ground black pepper
To serve, place a spoonful of each of the guacamole and salsa onto the plate. Place the monkfish alongside and finish with a few watercress leaves.