To assemble the salad, put three toasts in the bottom of the prepared salad bowl. Top with tomatoes and sprinkle with one-fourth of the basil mixture, one-fourth of the tuna mixture and one-fourth of the olives. Drizzle with 2 teaspoons of the oil and 1 teaspoon of the remaining vinegar. Add a layer of toasts, top with onions, basil mixture, tuna mixture, olives, oil and vinegar. Repeat the layering, using peppers in the third layer and cucumbers in the final layer.