The 20-year-old Moroccan impressed during a brief stint at Loftus Road towards the end of last season and Rangers boss Jim Magilton has beaten off competition from other Championship clubs to bring him back to west London.
"I've seen Adel plenty of times and I know he's a player of undoubted ability," said Magilton. "He's a match-winner on his day and will bring added competition to the squad.
"The fact we have been able to agree a deal to bring in someone of Adel's quality shows the sort of direction this club is heading in.
"If you can encourage a squad player from the Premier League to take a drop down to the Championship, then it shows what your intentions are."