Douglas John Hall, The Cross in Our Context: Jesus and the Suffering World. Augsburg, 2003.
Reflection on Zechariah and the two processions: http://dancingwiththeword.com/the-donkey-a-subversive-choice/ (hat-tip to the anonymous author of the weekly Gospel reflections from Christ and St Luke’s Church, Norfolk VA for pointing me here), which is in turn drawing on Borg and Crossan, The Last Week: What the Gospels Really Teach about Jesus’ Final Days in Jerusalem, Harper Collins 2007; which is now surely the most quoted source in Episcopal sermons on Palm Sunday.
Note on the graphic: created in Canva in about 10 minutes. Palm photo was free download from Pixabay.