Using a garlic press, press the garlic clove into a small bowl. Whisk in the mayonnaise and lemon juice. Spread one side of each slice of toasted bread with garlic mayonnaise. Divide Crispy Prosciutto over 4 slices; top each with 1 leaf romaine lettuce and thinly sliced plum tomatoes. Top with remaining bread slices, mayonnaise side down. Place in panini maker or serve cold according to your preference!