Four fire engines and around 25 firefighters were called to a fire at a restaurant with flats above on Sarnesfield Road in Enfield.
Part of the ground floor was damaged by fire and part of the ducting from the ground floor to the roof level was also damaged by the blaze. One man, one woman and three children left the building before the Brigade arrived. They were treated on scene by London Ambulance Service crews.
The Brigade's Fire Investigators believe the fire was caused by unattended cooking.
A London Fire Brigade spokesperson said: "Fires are more likely to start in the kitchen than any other room in the home.
"Cooking should never be left unattended on the hob or grill - if you have to leave the kitchen then turn off the heat.
"We'd like to remind restaurant and takeaway owners to make sure that they don't have dirty ducting.
"If you don't clean your extraction system regularly, you're at a greater risk of ducting fires."
The Brigade was called at 2109 and the fire was under control by 2244. Fire crews from Enfield, Chingford and Barnet fire stations attended the scene.