Place the pistachios, basil, arugula, oregano, garlic and cheese in a food processor. Pulse and blend until the nuts are coarsely chopped, then with the processor on, stream in 1/3 cup of olive oil. Add a little more if necessary, depending on how “spreadable” you want your pesto to be. Taste the pesto and add in the salt, blending once more. This will make a little extra pesto than needed, so store it sealed tightly in the fridge for up to a week.