Minted Mackerel and Mushroom Escabeche

Name: Minted Mackerel and Mushroom Escabeche
Ingredients: 4 (6-to 7-ounces) Spanish mackerel fillets; 2 tablespoons all-purpose flour; 1/2 cup plus 3 tablespoon extra-virgin olive oil, divided; 1 red onion, sliced into thin rounds; 1/4 pound mixed fresh wild mushrooms, sliced; 1/2 teaspoon coriander seeds, lightly crushed; 1/8 teaspoon hot red pepper flakes; 4 strips lemon zest; 1/2 cup dry vermouth; 3 tablespoons white-wine vinegar; 1 tablespoon fresh lemon juice; 1/2 cup coarsely chopped mint