If you prefer, have the fishmonger clean and fillet the sardines for you.Plus: More Appetizer Recipes and Tips
Arrange the sardines, skin side down, in a shallow glass or ceramic baking dish just large enough to hold them in a single layer. Scatter the sliced garlic and parsley sprigs all over the sardines. Pour 6 tablespoons of the olive oil along with the lemon juice on the sardine fillets, cover with plastic wrap and refrigerate, for at least 2 but not more than 6 hours. Drain the sardines, discarding the parsley and garlic, and pat dry. Transfer the sardines to a baking sheet.
In a small bowl, toss the chopped tomatoes with the remaining 2 tablespoons of olive oil. Season the tomatoes with salt and pepper.
Preheat the broiler. Toast the bread on both sides until golden and crisp. Rub the toast with the whole garlic clove, drizzle lightly with oil and transfer to a platter. Heat the sardines under the broiler for 20 to 30 seconds, or just until slightly warm; be careful not to cook the fish. Spoon the tomatoes on the bread and top with the fish. Sprinkle with salt and pepper and serve right away.
The recipe can be prepared through Step 1 up to 1 day ahead.