In a food processor, add the spinach, basil, garlic, cheese, salt, walnuts and lemon juice.
Turn on the food processor and slowly drizzle in the olive oil until the pesto comes together into a fairly smooth sauce. Be sure to stop processing while the pesto still has a little bit of texture to it.
Remove from the food processor and store in an airtight container in the fridge.
To store even longer, freeze small or individual portions until ready to use.