Smouldering bread was found on a disposable barbecue that caused a fire on 50 hectares of moorland.
Up to 70 firefighters tackled the blaze in Foulridge, near Colne, Lancashire, after flames from the barbecue set grass alight on Sunday.
The fire service said it had smouldering bread on it when crews arrived. No-one was injured.
It said those responsible were "not only careless but very irresponsible, ducking out" of reporting it.