The move by Africa's top-ranked team came less than 24 hours after Zahoui took charge of a 2-1 win over Mali in a warm-up and ahead of the visit of Tanzania on Saturday when the Ivorians begin their bid to qualify for a third straight World Cup.
The Ivory Coast also play Morocco away in Marrakech in Group C of the African qualifiers on June 9.
Adding to the surprise is the fact that the 40-year-old Lamouchi has no previous experience as a coach.
The former Inter Milan midfielder, who is of Tunisian descent but won 12 caps for France, has been a television pundit since ending his playing career three years ago.
A brief statement from the Ivorian Football Federation announced the change and thanked Zahoui for his work but gave no the other details of the swift and unexpected change.
Zahoui took the Ivorians to the final of the African Nations Cup in Equatorial Guinea and Gabon earlier this year where they went through the tournament without conceding a goal but lost on penalties to Zambia in the final.
Zahoui, the first African international to play in Italy's Serie A in the early 1980s, was criticised for their defensive approach by pundits who felt their much-vaunted lineup should have been more adventurous.
Zahoui took over from Sven-Goran Eriksson after the last World Cup and won against Italy in his first game in charge in London in August 2010.
His lost just once - a friendly in Poland - in 20 matches in charge with 16 wins and three draws.
Lamouchi played for AJ Auxerre before wearing the colours of Monaco, Parma, Inter, Genoa and Olympique Marseille, ending his playing days in the Middle East.