Four fire engines and around 25 firefighters were called to a fire at a restaurant with flats above on Lavender Hill in Clapham Junction.
Part of the kitchen at the rear of the ground floor and part of the rear flat roof were damaged by the blaze. One man left the building before the Brigade arrived. He was treated at the scene by London Ambulance Service crews.
Battersea Fire Station Sub Officer David Rose, who was at the scene, said: "The fire involved a wood-fired pizza oven and it was well alight when we arrived.
"It was an arduous job as it had spread to the roof but crews fought hard to tackle the blaze and their initial efforts stopped it spreading to the flats above.
"Crews did a fantastic job - fires involving roof voids can sometimes be tricky."
The Brigade was called at 2018 and the fire was under control by 2236. Fire crews from Battersea, Wandsworth, Clapham and Brixton fire stations were at the scene.
The Brigade's fire investigators believe the fire was accidental and the most likely cause was as a result of structural timber catching alight due to prolonged radiated heat from a wood-fired pizza oven - a process known as pyrophoric action.