Make sure you buy plain canned tuna that doesn’t have added high FODMAP ingredients like onion or garlic. You can use either tuna brined in water or oil, as long as you drain it well.
The amount of wheat in regular soy sauce is low FODMAP, however, if you are feeling concerned you can buy gluten-free soy sauce or use Tamari.
Make sure your Thai fish sauce doesn’t contain any added high FODMAP ingredients like onion or garlic.
I have recently started to add a bit of granulated sugar to this dish as I find it beautifully balances out all the savoury/salty ingredients. It’s a trick of Thai cooking. However, you can omit this if you prefer.