He was sacked by manager Paul Merson, who said he needed more experience, but later had coaching positions with Swindon, Lincoln and Gillingham.
Onoura also had spells as caretaker manager of all three clubs.
He was first-team coach with Gillingham and assistant to Peter Jackson at Lincoln but left Sincil Bank in 2008.
Onoura started his senior career with Huddersfield and went on to play for Mansfield Town, Gillingham, Swindon, Sheffield United, Wycombe Wanderers, Grimsby Town, Tranmere Rovers and Walsall.
He takes over the Walya Antelopes as they emerge from a time of turmoil in Ethiopian football.
The national team, who lie 123rd in the world rankings, were readmitted to international competition last year after a suspension that led to them being disqualified from the latest World Cup and Africa Cup of Nations tournaments.
In their last outing in the Africa Cup of Nations qualifying, Ethiopia finished bottom of their group.
There followed an internal feud over an attempt to sack Dr Ashebir Woldegiorgis as head of the Ethiopian Football Federation and that ultimately led to the Fifa suspension in 2008.
