Add the olive oil to a hot pan, then saute the cod cheeks with the chilli, garlic and spring onion. Season with salt and pepper.
Once the fish is cooked (about four minutes), remove from the heat and add the lime juice and zest.
Finely chop the remaining half of lime and cook gently in a separate pan to release the fruit sugars, until caramelised. Transfer the fish to a plate, garnish with the caramelised lime and serve with rice, potatoes or crusty bread.