Our first recommendation is Rutilio Grande: A Table for All by Rhino Guidos (copyright 2018). According to the Education for Justice description: "This new biography looks deeply into the life of [Servant of God] Fr. Rutilio Grande, SJ, whose passion for justice for those in poverty shaped Blessed Oscar Romero and many others during the long oppression and conflict in El Salvador." A reading guide for this book is available here.
This book is a timely addition to our knowledge of the life and work of Oscar Romero, whose canonization will happen in the fall.