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 time of year so many people need art activities for early finishers, art sub plans, and just plain art lessons, that are not specifically Christmas themed. Here are seasonal art lessons that will excite your kids in December or the winter.