To make the guacamole, combine all of the ingredients in a small bowl. Set aside, ready to serve in your lettuce cup tacos with the fish.
To prepare your crumb coating, whisk the eggs in a bowl with 3 tablespoons of water, then set aside. Put the tapioca flour in another bowl, and the almond meal in a third bowl.
Cut the flathead fillets into eight even portions and season them with a little salt. Dust the fish pieces lightly with the tapioca flour, dip them in the egg mixture, and then press them firmly in the almond meal until both sides are coated.
Put the coconut oil in a wok or large saucepan and heat it to 160°C. To make sure the oil is at the right temperature, drop in a small piece of fish. It should bubble instantly around the edges.
Fry the fish in batches, for about 90 seconds per batch, or until cooked through. Drain the fish on paper towel and season with salt.
6. Put the fish in a lettuce cup, give it a good dollop of guacamole and squeeze a little lemon juice over the top, then wrap to form the tacos.