Heat oven to 350 degrees F.
Heat oil in nonstick skillet. Add onion and garlic; cook until onion is very soft, 5 minutes. Add tomatoes, broth, wine, thyme, 1/2 teaspoon salt and 1/4 teaspoon pepper; simmer, uncovered, until sauce is reduced and thickened slightly, 5 minutes.
Season fish with remaining salt and pepper. Place in 13 x 9-inch baking pan. Add sauce; cover.
Bake in 350 degree F oven 15 minutes. Add spinach to sauce around fish. Bake 5 minutes or until fish flakes. Makes 4 servings.