Fire ripped through the ceiling of the Hungry Jacks restaurant in Kangaroo Flat on Saturday night.
Five units were called out to the fast-food restaurant at 8.12pm and took about an hour to control the blaze.
Kangaroo Flat fire captain Andrew Purdy said grease build-up in an overhead extraction fan was the cause of the fire.
There were no customers at the restaurant at time but several staff were evacuated.
Mr Purdy said it was a difficult fire to contain because of its position in the ceiling.
“We got it under control within an hour,” he said. “It wasn’t a large fire at the end of the day, just a difficult one to access due to the ducting.”
Mr Purdy said the fire was preventable and more could have been done to make sure the vent was free of grease.
“It (the fan) probably needs to be cleaned regularly and it seems it hasn’t been cleaned for a while,” he said.