Preheat the broiler. Rinse 4-6oz fish fillets in cold water and pat dry with a paper towel. Place the fish on a baking sheet or oven-proof skillet. Season with sea salt and the herbs de Provence, optional. Slather the tops of the fillets with 1 tbsp Dijon mustard. Combine 3 med heirloom tomatoes diced, 1/3 c olives, 1 tbsp capers, 1 clove minced garlic, 2 tbsp olive oil, 1 tbsp white wine vinegar, and ½ teaspoon salt in a medium mixing bowl. Drizzle the tomato mixture over the fish. Bake the fish under the broiler, rotating the pan halfway through for equal browning, for approx 10-15 minutes, or until the fish is cooked through and the tomatoes are slightly caramelized. Top with mixed chopped herbs parsley, thyme, or chives, optional, for garnish and serve immediately.