If using raw walnuts or sunflower seeds, toast in a dry pan over medium heat until slightly golden brown. Remove from the heat immediately. Don't burn them!!!
In a food processor, pulse the arugula, parsley, and walnuts or sunflower seeds.
With the processor running, drizzle in the olive oil until combined.
Add the pecorino Romano cheese and pulse a few times until just combined.
Store in a glass jar with a tight-fitting lid. Top with a little more olive oil to preserve.
If using a blender:
Add all the ingredients except for the cheese and blend on medium-low speed until combined.
Remove from the blender and fold in the cheese.
Store in a glass container with a tight-fitting lid. Top with a little more oil to preserve.