If I'm honest, I have really struggled with the challenge this week. The stitch was chain stitch which I have used many times before: most recently on the cover of my 2012 diary.
I like chain stitch but I really struggled to think beyond the straight or wiggly lines that are familiar. So here is my attempt - I didn't manage to fill the space but may have another go if inspiration strikes!
I had a go at a few shapes...
and patterns...
I will have to check out everyone else's ideas to see if there's anything else I can use this stitch for.