Former Guiseley AFC boss Bower was appointed in September 2016 and guided the club to National League North safety in his first campaign.
He took the helm again in the 2017/18 season and led Avenue to a seventh-place finish and into the semi-finals of the play-offs.
As a player, he made over 200 appearances for neighbours Bradford City and has now established himself as one of the best young managers in non-League football.
Boshell was Bower’s right-hand man during their time at Guiseley, combining a role in the dug-out with duties in the centre of the Lions’ midfield.
He assumed the same role upon joining Avenue in September 2016 and made twenty-eight appearances last season.