Broiled Mahi-Mahi With Parsleyed Tomatoes and Feta

Ingredients

• 2 onions , sliced
• 2 tablespoons olive oil
• 2 tomatoes , seeded and chopped
• 2 tablespoons fresh parsley , chopped
• 1/4 cup white wine
• 1 tablespoon tomato paste
• 2 garlic cloves , chopped
• 1/2 teaspoon salt , divided
• 1/2 teaspoon pepper , divided
• 36 ounces mahi mahi fillets
• 4 ounces feta cheese , crumbled
• 1 lemon , thinly sliced