Preheat the oven to 400 degrees. Core the tomatoes and thinly slice. Place in a colander in the sink and sprinkle with 1/2 teaspoon salt; let drain for at least 15 minutes.
Meanwhile, cook the bacon in a large skillet over medium heat until crisp, about 10 minutes; transfer to a paper-towel-lined plate. Pour off and reserve the drippings, leaving 1 tablespoon in the skillet; toast the bread on one side in the drippings until golden (do this in batches, adding more drippings as needed). Place the bread, toasted-side down, on a baking sheet.
Combine the cheeses with the mayonnaise, scallions and parsley in a bowl. Spread the cheese mixture on the toasts, reserving about 1/3 cup. Crumble the bacon on top. Shake any excess liquid from the tomatoes; distribute the zucchini and tomatoes among the toasts. Dot with the reserved cheese mixture and season with pepper. Bake until golden brown, 15 to 20 minutes. Serve warm.
Photograph by Antonis Achilleos
Courtesy of Food Network Magazine