Call the Shot?

My lime tree has a surprise growth that sprang up alongside it:


I reuse my soil year after year (thanks to many failed attempts), which include tomato, basil, pepper, avocado, cilantro, lavender, and green onion. Could it be one of those? Or is it an evil weed that I've been allowing to grow all this time?

All I know is that it is not the 1 plant I can identify in my sleep. Any ideas what this mystery sprout could be?