To make the fish tacos, Fill a deep-fat fryer or a large, deep, heavy-bottomed pan two-thirds full with the oil. Heat to 180C (a cube of bread should turn brown in one minute when dropped in.) CAUTION: Hot oil can be dangerous. Do not leave unattended. Mix the seeds, polenta and oats in a wide bowl. Mix the condensed milk, lime juice and salt together in a separate wide bowl, dip the fish in the condensed milk mixture and then in the seed mixture. Deep-fry for about 3–4 minutes, or until golden. Transfer to kitchen paper to cool slightly and chop into large pieces.
To make the tomato sauce, heat the oil in a large frying pan and sweat the onion and garlic. Add the chilli and tomato and cook for 5 minutes. Tip into a pestle and mortar and grind to a rough paste.
To serve, heat the oil in a frying pan and fry the tortillas until puffed and golden. Mix the mayonnaise and soured cream in a bowl. Once slightly cooled, flatten down the tortillas and fill with the tomato sauce, fried fish, mayonnaise mixture, avocado, coriander, pickled onions, lettuce and spring onions. Serve immediately.