Place a wide deep pot on the stove with at least 5-6cm of oil and place on a MED-HI heat (180°C).
Toss your fish pieces in Fish Spice and set aside.
Mix the flours and baking soda together in a bowl, leaving a well in the centre. Whisk together the soda water and egg, then mix gently into the flour to make a thin batter. Add in a few ice cubes to keep your batter cold.
Dip your fish, piece by piece into the batter, wiping any excess away before dipping gently into the oil. Hold the piece halfway into the oil for a few seconds before letting go (this stops the tempura from sticking to the bottom of the pot).
Cook each piece for 5-6 minutes or until golden.
Wash the watercress (leave in long tendrils). Toss watercress, pomegranate seeds and avocado cubes together. Dress with a 50:50 olive oil and lemon juice dressing.
Toss the fish pieces in Australian Chicken Salt before serving with watercress salad and lemon wedges.