Heat the oil in a pan over a medium heat. When the oil is hot, add the mustard seeds. Be careful as the mustard seeds will start to pop and splatter the oil.
Caution: Keep the pan well away from your eyes and face. Cover the pan with a lid and fry the mustard seeds for 20 to 30 seconds, or until they have stopped popping.
Add the onion, and fry for 3 to 4 minutes, or until golden brown. Add the ginger, garlic, and curry leaves, and fry for another 3 to 4 minutes, or until the garlic is golden brown.
Add the coriander, turmeric, chile powder, and garam masala, and stir until the mixture is well combined. Add the chopped tomatoes, grated coconut and the water. Bring the mixture to a boil, then reduce the heat to a simmer, cover the pan with a lid and simmer for 10 to 12 minutes, or until the ingredients have cooked through and the sauce has thickened.
Add the lemon juice, and chopped peanuts, and season well with salt, and freshly ground black pepper to taste. Add the salmon pieces, and continue to cook for 3 to 4 minutes, adding water as necessary to prevent the sauce from drying out, until the salmon is cooked through.
To serve, place one of the tortillas onto each serving plate. Arrange a thin line of the shredded lettuce down the center of each tortilla. Spoon over a portion of the salmon mixture and roll each tortilla up tightly into a sausage shape. Cut each wrap in half, and serve.
Cooks NoteThe longer you cook the masala, the better. Be sure to reduce it before you add the salmon, so that the finished filling is moist, but not too wet.