Hecking handed Nuremburg job
"There is fire within me. I am very eager to tackle my new post," Hecking, who worked at Hanover from 2006 until August this year, told reporters.
"I do not have to repeat that this is a very difficult situation. Just a look at the table proves that point."
Oenning, who took over in 2008, steered the team into Germany's top division in his first season but saw promoted Nuremberg lose their last four games without scoring a goal.
They are second from bottom of the Bundesliga with 12 points from 17 games after losing 3-0 at Cologne on Sunday.
The 45-year-old Hecking, who parted ways with Hanover after only two matches this season, was given a contract until the end of the season, with an automatic one-year extension should they stay up.
"Dieter Hecking is a coach who does not shy away from a tough job," said Nuremberg president Franz Schaefer. "I think we took a good decision to weather the second part of the season."
The Bundesliga resumes on Jan. 15 after a three-week winter break.