In a food processor, combine the avocado, sour cream, lime juice, garlic, parsley, and salt, and pulse until smooth. The consistency should be similar to sour cream - thick yet spreadable. To thin it, add a tablespoon or two of water and pulse to incorporate. Set aside.
Make black bean rotini pasta according to the instructions.
Serve about 3/4 cup of the black bean rotini with 1-2 tablespoons of avocado crema. Top with feta cheese crumbles and enjoy!
*The avocado crema will keep in an airtight container in the refrigerator for 1 day.