Sea bass with tomatoes, olives and capers

SEA BASS WITH TOMATOES, OLIVES AND CAPERS4 teaspoons olive oil, divided
4 (5-ounce) sea bass fillets (or other white fish)
1 small onion, diced
1/2 cup white wine (for the nine days use sparkling white grape juice or 4 tablespoons pareve chicken stock and 2 tablespoons fresh lemon juice)
1 cup canned low-sodium diced tomatoes, with juice
1/2 cup chopped pitted black olives
2 tablespoons capers
1/4 teaspoon dried crushed red pepper, optional
2 cups packed fresh baby spinach leaves
Salt and pepper1. In a large nonstick skillet heat 2 teaspoons of oil over a medium-high heat. Add fish and cook until opaque in the center, about 2 1/2 minutes per side. Transfer the fish to a platter and tent with foil to keep the fish warm.2. Heat the remaining 2 teaspoons of oil in the same skillet; add onion and saute for 2 minutes.3. Add the wine and cook until reduced by half, about 2 minutes. Add the tomatoes, olives and capers and crushed red pepper, if using, and cook for 3 minutes more.4. Stir in the spinach and cook until it is wilted, about 3 minutes. Season with salt and pepper. Spoon the sauce over the fish and serve.