Police said two males were seen breaking into the restaurant in Springvale, in Melbourne's southeast, about 12.15am on Sunday.
A spate of firebombings and arson attacks has swept the city in the past week, including an incident in which six cars were set alight at separate locations in a single night.
Fire crews arrived at the scene in the early hours of Sunday to find smoke billowing from the window of the restaurant.
The two males fled the scene in a car.
Shortly later, a teenage boy was found with burns at a fast-food restaurant in Heatherton, about a 10-minute drive from the Springvale fire scene.
Emergency services were called to the scene and treated the boy.
The 15-year-old was arrested and taken to hospital under police guard.
Police said a crime scene had been established and the investigation was ongoing.
Days earlier, a 13-year-old boy was left fighting for life after suffering burns to 90 per cent of his body during an alleged firebombing in Taylors Hill.
The boy was found in a vehicle after what police believe was an attempt to flee the site on Thursday.
Police have since arrested two 16-year-old boys and a 15 year-old boy for questioning over the incidents.
That incident was part of a busy night for investigators, who responded to reports of six cars being set alight in different locations.
Arson and Explosives Squad head Chris Murray told reporters during the week that police were committed to finding others involved in the Taylors Hill arson and holding them responsible for the teen's injuries.
"We have a young boy whose life is currently hanging in the balance," he said.
"Let me be clear: this is not a game - no amount of money is worth risking your future or your life. Lighting a fire means putting yourself in danger."
Victoria has experienced a spate of arson attacks on vehicles, homes and businesses which police believe is linked to organised crime.
Young people may be recruited online or over encrypted apps to carry out crimes on behalf of criminal syndicates.
In September, a 23-year-old man was found with severe burns in the carpark of a tobacco shop following an alleged firebombing in Melton, on the outskirts of Melbourne's northwest.
There have been more than 150 tobacco store fires in Victoria since March 2023.
22°C