Mohammed Zaman had denied manslaughter by gross negligence, perverting the course of justice and six food safety offences in relation to the death of 38-year-old Paul Wilson.
But a jury today found 53-year-old Zaman guilty of all charges except perverting course of justice after a trial at Teesside Crown Court.
He will be sentenced later today.
Lawyers for the prosecution told the court that Zaman had been "reckless" and replaced almond powder with groundnut mix, made from peanuts, to cut costs at the restaurants he owned.
More From This Section
He died three weeks after a teenage customer at another of Zaman's six restaurants suffered an allergic reaction, which required hospital treatment.
Prosecutor Richard Wright said: "His was a reckless and cavalier attitude to risk and one that we, the prosecution, would describe as grossly negligent.
"Time and again he ignored the danger and did not protect his customers. The evidence will establish that Mohammed Zaman put profit before safety and that he cut corners at every turn."
The court was also told that Zaman was almost 300,000 pounds in debt and cut costs by using the cheaper nut powder and by employing untrained, illegal workers.
"If you go to a restaurant, you don't expect to die from eating a meal. It's important owners have the right procedures, buy the right ingredients and employ the right staff to make up the meals."
Zaman's restaurant is called Indian Garden, a popular trend among Bangladeshi-origin restaurateurs to cash in on the popularity of Indian food in the UK.
Wilson's parents, Margaret and Keith, said their son was "meticulous" about dealing with nuts after had a reaction to a chocolate bar at the age of seven.