To make the sauce: Toast the coriander and cumin seeds in a dry frying pan until they start to pop, then crush them in a mortar and pestle or spice grinder. Add with all the other sauce ingredients to a saucepan and heat over low heat until hot. Remove heat and set aside for 2 hours, then strain and discard the spices.
Boil the potatoes until tender. Let cool, and cut into 2cm slices. Blanch the beans for 2 minutes. Preheat the oven to 180 degrees C.
Heat a little oil in a frying pan and cook the onions until golden brown. Set aside. In an oven dish, add some more oil and the potatoes and cauliflower. Season with salt and pepper and place in the oven for 15 minutes. Add the onions, green beans and sun-dried tomatoes and turn the heat to low.
Heat up some more oil in a frypan and fry the whiting fillets skin side down until golden. Turn the fillets over and remove from the heat. Season with salt and pepper, lemon zest and chopped parsley.
To serve, arrange the baked vegetables and the roma tomatoes on plates. Top with whiting fillets, the herb sauce, and sprinkle with chives, coriander and basil.