Place the walnuts in a food processor and pulse until they are thoroughly chopped. Add the garlic, basil, parsley, sun-dried tomatoes, Parmesan, salt, pepper, lemon zest, lemon juice, and balsamic vinegar. Pulse for a few seconds. With the machine running, add the oil in a steady stream to combine. Transfer the pesto to a serving bowl and use immediately, or cover and refrigerate for up to 1 week, or store in the freezer for 3 months.
Yield: About 1 1/2 cups