As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LHR INFLIGHT T107/20JAN - SMOKE COMING FROM FORWARD GALLEY OVEN. RETURNED TO LHR AND LANDED WITHOUT INCIDENT. FOUND DEBRIS BURNING IN OVEN. CLEANED DEBRIS AND PULLED AND COLLERED CIRCUIT BREAKERS. REPLACED FIRST CLASS OVEN NUMBER ONE AND TWO AT JFK. SYSTEM GROUND CHECKED NORMAL OPERATION.