Making a mustache/moustache to launch a writing prompt, is an interesting and "Suessical" way of doing things. I think your students will enjoy it.
For an adorable bulletin board, take everyone's photograph wearing their mustache and put it next to their writing. Your bulletin board title could be the same question you are asking: "We mustache you, would you save a truffula tree?" Flank the board on either side, with 2 colorful truffula trees, made out of strips of neon-colored tissue paper, and rolled up green bulletin board paper for the trunk, that you can stripe with brightly colored boarder.