Add in the vegetables, starting with the firmer ones which require more cooking (ie: carrots vs bell peppers) and reduce the heat to medium or so, to maintain a gentle rolling simmer.
After about two minutes, add the remaining vegetables, as well as the fish. Place the lid on the pot and let everything cook till the fish is just opaque, tender and flakey. Depending on the the thickness of the fish you are using, this could take only two to three minutes, turning over and then cooking the other side. Add thicker pieces of fish a minute before thin fish or shrimp.
Taste and adjust any seasonings. Do you want it sweeter, add a bit more sugar. Need it to be more savoury, add some tamari or soy sauce for umami depth. Salt will be in the fish sauce, so only add salt once the curry is done and you can taste it all together.
Depending on how thick you want the sauce, I share alternatives below in the notes.
Divide the rice between four bowls. Ladle fish and then the curry and vegetables evenly between the four bowls.
See blog post for more details and suggestions.
Start with the amount of curry paste stated, add more once you have tasted the curry sauce if you so desire. You can switch up the red curry paste for yellow or green curry paste, it will change the flavour, and the heat level may change, so adjust as you see fit.
Use full fat canned coconut milk, not the type found in a carton meant for drinking or adding to smoothies etc.
*Change the ratio of coconut milk to stock to create a thicker, creamier curry. You can also add in a cornstarch slurry (either 2 tsp cornstarch in 1 tsp cool water, or 1 tbsp cornstarch whisked in 2 tsp water, depending on how thick you want the sauce) and stir it through the simmering sauce till smooth and gently thickened. Add it in once you remove the fish, whisk it gently through.
You can use fish stock if you have that on hand as well.
For a full choice of vegetables, see the blog post. Ensure that the vegetables you choose are all chopped or julienned in similar sizes for even cooking. If you are making a vegetarian version, feel free to increase the amount of vegetables you are using.
Feel free to use any firm white fish you desire, or even shrimp etc. You can even combine them in one curry. You can also replace the fish with chicken or even tofu. See blog post for full list.
Garnishes are all a suggestion, the lime, scallions and cilantro are classic and will balance the flavours. The heat options are as you desire.