A TEENAGER beat his mother to death after she told him to eat his vegetables, the High Court heard yesterday. Lau Chi-man, 44, died of head injuries after her only son, Cheung Wing-chuen, 17, lashed out in a fit of rage. Cheung, 16 at the time of the attack, admitted one count of manslaughter. The court heard Lau had fainted after the assault in May last year, but appeared to recover after being violently sick. Two days later, she was discovered unconscious on the floor of the family flat by her husband, restaurant manager Cheung Fuk-yui, 42. Lau, a cashier at her husband's restaurant, fell into a coma and died in the Queen Elizabeth Hospital a day later, on May 17, 1993. Yesterday prosecutor Harish Melwaney said: ''The victim scolded the defendant for not eating more vegetables. He became angry and told her not to scold him. She became angry and hit the defendant's hand. He fought back, pushed her to the ground and hit her on the face several times. She then fainted.'' But defence counsel Yeung Yeuk-chuen said the killing was ''a family tragedy rather than a crime as such''. Mr Yeung said the teenager, who had been slightly brain-damaged since birth, had lashed out after months of bottling up his frustration. Deputy Judge Cheung adjourned sentencing for medical reports.