Skim the coconut cream of the top of the coconut milk and heat or alternatively heat a few tablespoons of vegetable oil in a heavy pot over medium heat.
Add the red curry paste and fry until fragrant. Add the coconut milk and water.
Add the rest of the ingredients besides fish sauce and sugar. Bring the sauce to a gentle boil, stirring well to break up the tuna chunks. Simmer for a half hour or longer, until the herbs have released their aroma and the oil comes to the surface.
Season with fish sauce and a little bit if sugar to taste. If the tuna was very salty, the sauce might not need any additional seasoning at all.
For the Garnish:
Boil the noodles according to instructions until soft. Drain and put into a pot of cold water. Pull a few fingers full of strands out at a time and wrap them around your fingers, thereby creating little nests. Squeeze the little nest gently to rid it of all the water. Lay on a serving platter. Repeat with the rest of the noodles.
Serve noodles, rest of the garnish and the heated sauce together, so everybody can assemble their own plates according to their taste.