Sub Lesson with Patterns and Initials
Mrs. Danno at Grande Park Elementary in Chicago posted this fourth and fifth grade lesson. She intended it as a two part lesson that she would teach. The first lesson was when she introduced the idea of zen doodles and they practiced creating designs. In the second lesson, they created the design with a letter and patterns. I think a sub could teach a version of this in one class by just doing what was intended for lesson 2, but certainly you can do the lesson as she suggested.
This blog post includes multiple visuals and instructions. You may find this lesson at the her blog: 4th and 5th Grade Zentangle Letters.