San Mateo County Supervisor Adrienne Tissier is conducting a foreclosure workshop for at-risk homeowners next month. The free event, held for the first time last year and in conjunction with the San Mateo County Housing Leadership Council’s annual Affordable Housing Week, will provide advice for avoiding scams that prey on desperate homeowners. The workshop is May 15 from 9:30 a.m. to 1 p.m., at Parkway Heights Middle School in South San Francisco.