Make the salsa verde first. Place the coriander, basil, spring onions, chillies and garlic in a food processor and pulse until well chopped. Add in the fish sauce, lime juice, salt and pepper. Pulse again to combine.
Heat the oil in a very large frying pan (skillet). Season the cauliflower with the salt and pepper and place in the hot pan. Fry on one side for 2-3 minutes until well browned, then turn over. Fry for another minute, then add in the stock. Bring to the boil and simmer for 3-4 minutes until the cauliflower is tender (if you need to do this in two 2 batches, keep the first batch warm in a low oven).
Place the cauliflower on a large serving plate and spoon on the salsa verde. Serve with a bean or leafy salad.