Both men died as a result of their crash injuries.
Mr Gulmez and Mr Joubert had been travelling around New Zealand independently, but met in Wellington and agreed to travel from there to Nelson together.
The inquest heard that Mr Gulmez's car, a 1992 Mitsubishi RVR stationwagon, had been modified - likely before he bought it.
The rear seats had been removed and replaced with a piece of particle board so that luggage could be stored underneath and passengers could sit or lie unrestrained on top.
It was there that Mr Joubert had been sleeping when the crash happened on the morning of December 5.
Coroner Scott heard that they had been travelling behind a truck in a line of traffic when the car did "a bit of a zig-zag", according to witnesses.
Around 34 metres before the impact area, police crash investigator Senior Constable Simon Burbery found a 'seal push' - a raised ridge of tar-seal just to the right of the left-hand white fog line often caused by hot weather.
He said driving along the ridge surface at the road edge could have an "unsettling effect" on drivers.
Coroner Scott agreed that it likely played a part in the fatal smash, as Mr Gulmez drove onto it while he distracted by preparing to eat spaghetti.
"He was not concentrating on driving and the car drifted left, hitting the area of seal push," Coroner Scott said.
"This caused a wobble or a shimmy and the combined effect of this plus the general lack of concentration while preparing to eat the spaghetti caused Onur to lose control of the car. It veered right and collided with the approaching utility vehicle."
Coroner Scott said the New Zealand Land Transport Authority may consider issues in his finding relating to seal push.
While they may already be aware of the phenomenon and will address it "as and when appropriate", he hoped they would take on board his comments that it caused or contributed to this crash.
The coroner offered his sincere sympathy and condolences to both families of "young men who died so far from home".
