the mayonnaise, lemon juice, and zest in a small bowl to blend
. Set the mayonnaise mixture aside.
Toast the bread on a panini grill
until golden brown. Spread the mayonnaise mixture over each slice of toast. Arrange the prosciutto over the toasts, dividing equally. Top with the arugula
, then the tomatoes
the oil over the sandwiches, then sprinkle with salt and pepper. Cut the sandwiches into 3 equal pieces and serve.