Legitimate public health organizations have not recommended avoiding non-vegetarian food after getting inoculated. The claim is baseless.
The U.S.'s Centers for Disease Control and Prevention (CDC), the U.K.'s National Health Service (NHS), and India's Ministry of Health and Family Welfare (MOHFW) offer information for people who have been newly vaccinated. However, they focus on the vaccine's safety and side effects and do not advise on the type of food to be consumed.
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19 including symptoms, prevention and available treatment, please refer to the World Health Organisation or your national healthcare authority.