Heat 1 tablespoon of butter into a large skillet. Saute onion for 2 minutes until soft and add garlic to saute for a further 1 minute
Add tuna into the pan and separate it using a spatula
Add rice and fresh herbs; then saute everything until well combined and no more clumps
Add fish sauce, stir again for a further of 1-2 minutes until well combined
Adjust seasonings and serve immediately