Place the pine nuts in a small dry skillet over medium-low heat.
Toast for 2–3 minutes, stirring frequently, until lightly golden and fragrant. Transfer to a plate and allow them to cool.
Add the sun-dried tomatoes, basil, Parmesan cheese, toasted pine nuts, garlic, lemon juice, red pepper flakes, and black pepper to a food processor.
Pulse several times until the ingredients are finely chopped, stopping to scrape down the sides of the bowl as needed.
With the food processor running, slowly pour in the reserved sun-dried tomato oil.
Continue blending while adding the olive oil, 1 tablespoon at a time, until the pesto reaches your preferred consistency. Leave it slightly textured for spreading or blend it longer for a smoother sauce.
Taste and add salt only if needed. The sun-dried tomatoes and Parmesan may already provide enough salt.
Transfer the pesto to a serving bowl or airtight container. Serve immediately or refrigerate until ready to use.