Remove spines from lime leaves and shred finely. Wash and finely chop coriander roots. Reserve coriander sprigs. Combine lime leaves, coriander roots, chillies and coconut milk in a ceramic dish. Add salmon fillets and turn to coat. Cover and refrigerate for 30 minutes.
Halve cucumbers lengthways. Remove seeds with a teaspoon. Finely dice cucumber and place into a bowl. Remove cheeks from mango, scoop out flesh and dice. Add mango to bowl with cucumber. Chop half the reserved coriander sprigs. Add to the mango and cucumber mixture.
Preheat a BBQ plate on high and grease with oil. Remove salmon from marinade and cook skin-side up, on plate for 2-3 minutes or until golden. Turn and cook for 2-3 minutes or until cooked to your liking. Serve salmon with steamed rice, cucumber salad and a lime wedge.