Heat 1 tablespoon of oil in a large, heavy based saucepan and fry eggplant until golden. Set aside.
Coarsely chop all the curry paste ingredients and blend to a paste. If you do not have a blender, or for a more rustic texture, pound to a paste in a mortar and pestle and separately, finely chop the onion.
Heat another tablespoon of oil in the same (now empty) saucepan and when quite hot (but not smoking), add the curry paste (and onions if separate) and fry, stirring fairly often, until fragrant and beginning to caramelise slightly (become golden).
Add kaffir lime leaves and stir to heat through. Add coconut milk and water and bring to the boil. This is a good time to coarsely chop your coriander and thai basil leaves and put them in a small serving bowl for people to sprinkle over the curry.
Stir in zucchini, mussells and snapper chunks and simmer with the lid on until fish is just cooked and mussells have opened (about 10 minutes, but go by sight rather than relying on a timer to avoid overcooking your seafood). Stir through whole cherry tomatoes and fried eggplant.
Serve in large bowls spooned over steaming white rice, sprinkled with your fresh chopped herbs.