A panel discussion about the roots of Lexington’s break from Cambridge in 1713 will be held at 7:30 p.m. Friday at First Parish in Lexington, 7 Harrington Road. “Becoming Lexington” is part of a full slate of events commemorating the 300th anniversary of the town’s incorporation. The Rev. Peter C. Boullata, the minister at First Parish, will moderate the discussion by Richard Kollen, a retired Lexington High School teacher; First Parish member Charlie Bowen; and Sam Doran, a local historian. They will cover more than 10 years of efforts by farmers that led to the founding of Lexington as an independent community.