Arrange bread in a single layer on a baking sheet; broil 3 minutes or until toasted. Turn bread slices over; spread butter evenly over bread slices. Broil an additional 2 minutes or until toasted.
Combine arugula and shallot in a medium bowl. Drizzle arugula mixture with oil and vinegar; sprinkle with pepper. Toss well to coat. Divide arugula mixture evenly among 4 bread slices, buttered side up; top evenly with prosciutto. Divide pear slices and cheese evenly among sandwiches; top each sandwich with 1 bread slice, buttered side down.