Forrest's appearances have been limited under Ange Postecoglou, but seized upon a rare start as Celtic bounced back from their elimination from the Champions League after a 2-0 defeat by RB Leipzig in midweek.
"I was really strong on the fact that, if we put on a performance like we did on Tuesday, the goals would come and the quality of our goals was great," said Postecoglou.
"It's why I thought some of the Champions League comments were ridiculous. We set out to play a certain way and we've fallen short in areas where, for the most part, I think we can improve, but it's not through a failure of endeavour or will.
"We will never change our approach and the players wanted to show that today."
Forrest opened the floodgates after just nine minutes with a fine finish from Sead Haksabanovic's cross.
Giorgos Giakoumakis then swept home a second before Forrest's strike slipped through the hands of David Marshall as Celtic raced into a 3-0 lead after 25 minutes.
Elie Youan pulled a goal back for the visitors early in the second half, but Forrest's deflected strike completed his hat-trick to end any hope of a Hibs fightback.
Instead, Celtic extended their lead as Giakoumakis grabbed his second of the game before substitute Daizen Maeda silenced his critics by striking a sixth late on.
