The 25-year-old was reuniting with her former side for the first time since she left in January 2017, after a season spent with the North London side.
With the first return to Meadow Park, Oshoala shone brightly as she fired the visitors in front after Patri Guijjaro cancelled Katie McCabe's opener before half-time.
Five minutes after the restart, the Nigerian extended the tally for Lluís Cortes' side before Claudia Pina's brace overshadowed Kim Little's effort from the spot.
With today's brace, Oshoala has now scored six goals in three matches for the Liga Iberdrola side - fantastic form she will hope to take into the new season which begins on September 8.
The win over the English champions placed Barcelona in a great mood as they continue their pre-season against French top-flight side Montpellier on Sunday.