1. Preheat the oven to 400°F.

2. Spread the onions and orange zest in a large (13 × 9-inch) roasting pan; drizzle with the olive oil; season with salt and a grinding of black pepper. Roast for 15 minutes, stirring once. Add the figs (if using dried, see the Variation below) and half of the oregano. Roast until the onions begin to brown at the edges, about 10 minutes. Remove the pan from the oven. Increase the oven temperature to 450°F.

3. Push the onions and figs to the side in the pan and add the halibut. Drizzle the orange juice over the fish. Sprinkle with the remaining oregano and salt and pepper to taste. Spoon some of the onions on top of the halibut. Return the pan to the oven and roast until the fish is cooked through, 10 to 12 minutes.

4. Serve at once, with the roasted onions and figs spooned over the fish.

Variation with dried figs: Trim off the stems of 8 dried Calimyrna or Black Mission figs. Combine the figs and 1 cup water in a small saucepan and heat to a boil. Cook, covered, over low heat until the figs are plumped and tender and most of the water has been absorbed, 20 to 25 minutes. Cool; then drain and cut the figs in half The figs can be prepared 2 or 3 days ahead and refrigerated, tightly covered, until ready to use.