You could also serve this dish with a side of some steamed basmati rice. This is a simple dish with amazing flavour.
Preheat oven to 375 degrees F.
For the roasted tomato salsa: add a splash of olive oil, tomatoes, pearl onions, grated zest and juice of lime, and thyme sprigs to a medium roasting pan. Season the tomatoes with salt and pepper. Roast in oven just until onions and tomatoes start to soften, about 7 to 10 minutes.
Meanwhile season fish with salt and pepper, zest from 1 lime and chopped thyme. Add 2 tbsp. olive oil to large skillet or sauté pan over medium high heat. When pan is hot, sear fish on both sides, about 1 to 2 minute per side.
Transfer halibut to roasting pan after vegetables have roasted for about 7 to 10 minutes. Roast fish with vegetables, moving vegetables in the pan to surround the fish. Continue to roast until fish is cooked through and firm, about 7 to 9 minutes. Serve fish and roasted salsa with fresh watercress. Drizzle each plate with some of the pan juices.