Cut off the top 1/2-inch from the core side of the tomatoes. Using a spoon, scoop out the seeds and flesh surrounding them, leaving the exterior intact in a bowl shape.
In a small bowl, mix together the olive oil, vinegar, anchovies and garlic. Doing this will help disperse the anchovies evenly with the rest of the mixture.
In a separate bowl, combine the tuna, cucumbers, parsley, olives, tomatoes, capers, onions and shallots. Season with salt and pepper and dress in the anchovy mixture. Add more olive oil as needed to moisten the mixture, but it should not be wet.
Divide the filling among the tomatoes and top with some Toasted Garlic and Herb Breadcrumbs and shaved ricotta salata.
Toasted Garlic and Herb Breadcrumbs:
Cut the crusts from the bread and tear it into small pieces. Place in a food processor and pulse until a coarse-crumb consistency is reached. In a large skillet, heat the butter and olive oil together over medium-high heat. Add the breadcrumbs and toss to coat and continue to cook, stirring constantly. When the breadcrumbs begin to brown, stir in the parsley and garlic, and toast until golden brown, an additional minute. Remove from the pan and cool.