Tomato Toast with Tinned Fish

Name: Tomato Toast with Tinned Fish
Ingredients: 1/2 cup mayonnaise; 1/2 clove garlic, grated; 1/2 teaspoon grated lemon zest, plus 4 teaspoons lemon juice; 4 1/2-inch-thick slices sourdough bread; 3 heirloom tomatoes, sliced about 1/4 inch thick; Flaky salt and freshly ground pepper; 2 tablespoons finely chopped fresh chives; 1 tablespoon extra-virgin olive oil; 4 cups baby arugula; 3/4 cup fresh parsley; 4 ounces manchego cheese, sliced into 8 pieces; 2 4- to 6-ounce tins or jars of fish (such as smoked mussels in tomato sauce or oil-packed tuna)