MBTA officials are vowing to recoup the more than $34,000 — and counting — a Mattapan trolley driver has collected in workers’ compensation since, police say, he paid a friend to don a Halloween mask and attack him in a “phony” on-the-job assault.Thomas Lucey, 46, is facing charges of insurance and workers compensation fraud, among other counts, in connection with the bizarre plot, which police say crumbled when they lifted fingerprints off a fake plastic pumpkin his “attacker” left behind and traced them back to Lucey’s friend.