A BALANCED diet just doesn't happen. It takes planning and up-to-date information. So does getting the best nutrition out of a meal or eating right to enhance sports performance. Get a jump on a healthier lifestyle before summer. ''Healthy Eating, Healthy Living'' is a course that's being offered by the Open Learning Institute of Hongkong. It will introduce the basics of diet, nutrition and menu planning. Special nutritional needs, such as sports training and dietary concerns of the aged, the young and less mobile, will be discussed. The six afternoon sessions (around 21/2 hours each) begin on Saturday, May 8, at 2pm. The course will be taught at the institute (Mongkok), in English, and is limited to 20. The fee is $695. Contact: Dorothy Lai on 789-6663. WITH the plethora of cooking classes in May, maybe cooks will stay home and revive the art of home entertaining. Treks into the aromatic world of rogan josh, chicken tikka and dal continue at the Koh-I-Noor Restaurant with classes every Wednesday and Saturday afternoons. Menus rotate. For details, call the Central restaurant on 877-9706 . FANCY decorating your birthday cake? Let the staff of Baker's Dozen show you how. A series in cake decorating for beginners will be held on May 3, 4 and 5 from 9.30am to 12.30pm. The fee ($1,200) covers instruction, recipes and the use of tips . Advance reservations are necessary. Baker's Dozen, 1 Lan Kwai Fong, 6th Floor, Central. Telephone: 826-9283 or 826-9279. THOUSANDS of Australian notdogs have arrived by ship in Hongkong ready for an experimental run in the territory's supermarkets, writes Beryl Cook. The ''notdogs'' are a vegetarian product made by Australian firm Vege Fresh Pty Ltd and are expected to be distributed through Dragon Race Pty Ltd to the territory's supermarkets, starting next week. Queensland Government Office marketing manager, Mr Lucas Leung Ching-shan said the notdogs would be promoted in the territory first, but could also be released in China later. Hate to cook alone? Gather a team and head for Portico Restaurant at Citybank Plaza. Chef Franz Kranzfelder offers specially-designed classes for groups of 10. The $550 fee includes instruction, recipes, dinner and wine-tasting. Telephone: 523-8893. WHAT were you doing on May 4, 1988? Barry Kalb, for one, was selling spaghetti with tomato sauce and fresh basil for $50, veal in Marsala for $60 and home-made Italian ices for $15 at his then-new Ristorante Il Mercato in Stanley. Times have changed and Mr Kalb has expanded his business into a group of restaurants. To mark the fifth anniversary, he will ignore inflation for a day and offer signature dishes and pizzas at the original 1988 prices, on Tuesday, May 4 at Stanley, Central and Sai Kung.