Mats Seuntjens broke past the Fortuna back-four and took the keeper out of the equation with a cross six-yard box pass to allow Unal to simply roll the ball into the back of the net.
Unal scored his sides second goal in what turned out to be one of their most convincing wins of the season.
The victory took NAC Breda into fourth place in the Dutch second-tier 15 points behind leaders Sparta Rotterdam.
Unal joined NAC over the winter transfer window after an unsuccessful spell on loan at Belgian side Genk.
The Turkish international youngster joined City on a £2,000,000 move from Bursaspor over the summer transfer window.
The 18-year-old striker was forced to leave City on loan after failing to gain a work visa to play in England.
In 2013, aged 16, the City wonder-kid became the youngest player to score in the Turkish top flight, finding the back of the net in a match against Galatasaray.