It is parsley abundance season up here right now. I grow the curly leaf and the Italian flat leaf. They grow like crazy, and sometimes give you a second year after a milder winter.
"Pesto" means "paste." Sure, basil besto is delicious on lots of things and everybody loves it on vegetables, pasta, chicken, fish, whatever. But if you have lots of parsley, try a parsley-walnut pesto. It is perfect for grilled beef along with everything else you might use pesto for.