Cut the seabass fillets into ½cm wide strips. Place in a non-reactive bowl and sprinkle with the salt, stirring to coat evenly. Leave to sit for 1 minute, then pour over the lime juice and chilli and stir to combine. Cover with clingfilm and leave to sit in the fridge for 2 hours, stirring occasionally.
Preheat the oven to 200°C/gas mark 6. Cut the tortillas into 16 triangles and spread over two wide baking sheets. Drizzle with the oil and bake for 10 minutes, until golden and crispy. Transfer to a wire rack to cool.
Stir the diced onion, cucumber, tomato and coriander leaves through the fish. Season with pepper and serve with the tortilla crisps.