First you will prepare the dressing with the combination of chopped chillies, fish sauce, sugar and lime juice by placing them in a small bowl. After combining these ingredients leave them aside.
Then, take salmon and use olive oil to rub it in a baking tray. After rubbing it place the salmon in a preheated microwave oven and bake it for 20 minutes or until it can be easily flaked. When the baking is done allow salmon to cool down for about 15 minutes at least.
After that take a large bowl and put salmon into it. Now grab a fork and break this fish into large pieces. Then add basil, onion and tomatoes to it and subsequently put the dressing over salmon and other ingredients. When the dressing is poured then, toss this mixture lightly until gets mixed well.
Take lettuce leaves and put them in a plate and then, place this salmon mixture over them after which you can serve this salad immediately.