- Finely chop the red onion and transfer to a small bowl. Cover with ice water and soak for 5 mins. Drain well then set aside.
- Meanwhile, prep the following ingredients: 1) Finely chop the chilli. 2) Dice the cucumber into ½ cm cubes (roughly). 3) Dice the mango into ½ cm cubes (roughly). 4) Juice the limes and measure out the juice. 5) Juice the orange and measure out the juice.
- Cut the fish into 1 cm cubes and transfer to a medium bowl. Season with ½ tsp sea salt, toss gently to combine and leave for 2 mins.
- Meanwhile, combine the red onion, chilli, lime juice and orange juice in a small bowl; this is the marinade.
- Pour the marinade over the fish and toss gently to combine. Cover and leave to marinate in the fridge for 30 mins.
- While the fish is marinating, roughly chop the fresh coriander.
- Strain off the marinade. Add the cucumber, mango, fresh coriander and olive oil and combine. Taste and season with salt, if necessary. Divide the ceviche between bowls and serve immediately.