Montpellier head coach Patrice Collazo will join Foster as assistant coach.
The match will take place at San Mames Stadium on June 22nd, which last hosted the European Rugby Champions Cup Final in 2018.
Maxime Machenaud (Bayonne & France), Camille Lopez (Bayonne & France), Mako Vunipola (Saracens & England), Semi Radradra (Lyon & Fiji), Billy Vunipola (Saracens & England), Tevita Tatafu (Bayonne) are already confirmed to play in the World XV squad.
"We are delighted to host this historic match... which undoubtedly enhances the growth of rugby in our country," Spanish Rugby Union President Juan Carlos Martin 'Hansen' said in a statement.