Wash and pick through your arugula to make sure all the leaves are nice and healthy. I noted 2-3 cups because I initially added 2, but decided I wanted to bulk it up and added another big handful. Figure out what sort of leaf-to-nut ratio you like!
In a food processor, add the arugula, nutritional yeast, oil, cashews, salt, and pepper.
Peel and roughly chop the garlic so it's easier for the food processor to break it down. Add to the other ingredients.
Juice the lemon (about 1/4 of a small lemon) and add.
Blend on high, scraping the sides occasionally, until you have a nice spreadable pesto.