Sautée the onion and garlic in the oil until translucent.
Add lemon grass and fry together. Remove from pan and set aside.
In the same saucepan, fry the salmon pieces on each side until brown. Reduce heat.
In a blender, place the sautéed onion and lemon grass, the coconut milk, tamarind, tomato relish, sugar and salt and masala.
Add a cup of water. Blend and pour into the pan.
Above the salmon in the pan, place the pineapple, the tomato slices and the ginger gratings and bring to a simmer. Cook for an extra 10 min on medium heat.
Serve with basmati rice.