Trim the monkfish tail until the bone slightly protrudes and press the flesh down.
Mix chillies, garlic, lime zest, lime juice, coriander, olive oil, salt, and pepper in a bowl.
Coat the monkfish in the marinade and refrigerate for 2 hours.
Bring the fish back to room temperature before cooking.
Preheat the oven to 200°C.
Sear monkfish tails in a hot ovenproof pan then roast in the oven for 4-6 minutes.
Rest the fish for five minutes after cooking.
Blend all guacamole ingredients in a food processor into a coarse puree.
Combine salsa ingredients in a bowl and season with salt and pepper.
Serve monkfish alongside the guacamole and salsa, garnished with watercress.