The Planning Board at its meeting Thursday will hold a public hearing into a proposal by Lahey Clinic Foundation to install a gas-fired cogeneration plant at Lahey Hospital & Medical Center, 41 Mall Road. The 3-megawatt plant would supply the Lahey facility with about half of its electrical power. Lahey would obtain the fuel by tapping into a nearby natural gas pipeline owned by Tennessee Gas Pipeline. Lahey is seeking two special permits and site plan approval for the project. In some of its other business, the board will hold a public hearing into a special permit application by a local chiropractor, Matthew C. Guy Jr., to use 44 South Bedford St. for a home occupation. Guy wants to move his practice from 165 Bedford St. The board will hold a hearing into a special permit application by Besito Restaurants to open one of its Mexican restaurants in the Burlington Mall. It will also continue a public hearing into an application by Liscotti Development Corp. for site plan approval and three special permits for a mixed-use development at 201 Middlesex Turnpike. The meeting will be held at 7:30 p.m. in Town Hall.