Januzaj, 19, has made five substitute appearances this season but made his point to Van Gaal, watching on from the directors' box at Old Trafford on Monday night.
Januzaj slots away one of his three strikes on Monday night
The Belgium international, who has scored four times for the first-team, was withdrawn after an encouraging 83 minutes in a 4-0 victory. His compatriot Andreas Pereira also got on the scoresheet.
Luke Shaw, yet to make his senior debut, made his first home start for United, whose line-up included Anderson ahead of the weekend trip to Leicester City.