The Planning Board on Thursday will continue a public hearing into a special permit application by the Lyons Group to open an Italian restaurant at 19 Third Ave. in Northwest Park, off the Middlesex Turnpike. The 240-seat restaurant would be part of the 3rdAve development of high-end restaurants, stores, and eventually housing that Nordblom — which controls the land — is creating in the business park. The proposed restaurant would occupy 6,000 square feet of a planned 13,000-square-foot building. The Lyons Group owns Scampo, an Italian restaurant in Boston’s Liberty Hotel, and Sonsie restaurant on Newbury Street in Boston, according to Douglas Wynyard, Nordblom’s senior vice president. The Lyons Group also owns the Kings restaurant and bowling alley chain, and plans to open another of those establishments this spring in a building now being renovated on Second Avenue in Northwest Park, part of the 3rdAve project.