Heat the olive oil in a frypan over medium heat; place the cumin and mustard seeds in the hot oil and cook until the seeds begin to pop. Cook and stir the onions in the spice mixture until they brown. Mix in the garlic, ginger, chilli and curry leaves; cook and stir until the garlic becomes golden.
Add the tomatoes and stir for a few seconds before adding the salmon, using the back of your stirring spoon to break the salmon into small pieces in the pan; cook until the salmon is heated through, 5 to 10 minutes; remove from heat. Garnish with coriander to serve.