NAC crushed Fortuna Sittard 5-0 at home to record their eight home win of the season.
Ünal scored the fifth and final goal on 64 minutes with a lovely finish from just outside the six-yard box.
The victory took NAC into third place in the Dutch Jupiler League 12 points off leaders Sparta Rotterdam.
Ünal joined NAC Breda on loan after cutting his temporary move to Genk short last month.
The striker joined Genk on a two-year loan over the summer after joining City on a £2 million transfer due to not having the necessary work visa requirements to play in England.
Ünal joined the Premier League giants as one of the most promising players to emerge from Turkey recent years and holds the record for being the youngest player to have scored in the Super League – against Galatasaray aged 16.