Preheat the oven to 350°F. Spread the tomato halves in a single layer on an oiled baking tray, cut side up. Whisk some sea salt, black pepper and thyme into a little olive oil, with some vinegar and garlic if desired. Brush liberally over the tomatoes. Roast for 15 minutes, then reduce the oven temperature to 250°F and roast the tomatoes for a further 1–1½ hours, or until shriveled but juicy. The tomatoes can be prepared in advance and stored in a sealed container in the refrigerator until required.

To make the chili and mustard dressing, heat the peanut or olive oil in a small saucepan until very hot. Add the mustard seeds and cook for 2–3 minutes, or until they start to pop. Add the garlic and cook until golden and beginning to crisp. Add the chili and ginger and cook for a further 2 minutes. Remove from the heat and stir in the palm sugar, fish sauce and lime juice to taste. Set aside.

To make the beurre blanc, combine the vinegar, wine, shallots, peppercorns and bay leaf in a small saucepan over medium heat. Bring to a boil and cook until the liquid reduces by two-thirds. Strain into a clean saucepan, return to heat and whisk in the cream and saffron threads.

Return to a boil and cook until the liquid reduces by one-third. Briskly whisk in the butter, one piece at a time. The sauce should be thick and glossy. Adjust to taste with the lemon juice and season with sea salt and white pepper. Keep the sauce warm but not on direct heat (a thermos is ideal).

Preheat the grill to hot. Dust the fish fillets with flour and shake off any excess. Put the fish on a greased baking tray, brush lightly with clarified butter and season with sea salt and black pepper. Grill for 8–10 minutes, or until just cooked but still moist.

Meanwhile, heat a little clarified butter in a large, heavy-based frying pan over high heat and sauté the zucchini briefly, until tender. Season with sea salt and black pepper. Add the roasted tomatoes to one side of the pan to warm through.

To serve, divide the zucchini among serving plates. Place a fish fillet on top and drizzle the saffron beurre blanc around each plate. Rest two warm tomato halves on each fish and scatter with coriander. Stir the chili and mustard seed dressing well and generously spoon over the tomatoes.