Deseed and very finely chop the pepper, and trim and finely slice the spring onions, then add to a bowl. Slice the fish into 1cm cubes, add to the bowl, then cover and place in the fridge until needed. Squeeze the lemon juice into a jam jar, add 1 teaspoon of sea salt, then seseed, finely chop and add the chilli. Pop the lid on and place in the fridge to chill – this may seem like a lot of salt but most of it gets drained away. Pick the herbs and cress, and place in the fridge. You can assemble the ceviche just before your guests are ready to eat, but it’s important that you don’t leave the fish marinating for too long – you don’t want the acids in the juices to cook the fish. Pour the lemon dressing over the fish mixture and immediately mix it up. Leave it to sit for about 2½ minutes while you lay out the plates. Throw most of the herb mixture into the bowl with the fish and very quickly toss it together – no more than 10 seconds. Divide the ceviche between 4 plates, gently spoon over a little of the dressing (discarding the rest) and sprinkle with the remaining herbs. Drizzle over a little oil from a height, sprinkle with freshly ground black pepper, and enjoy.