Cook the pasta according to the package instructions until al dente. Reserve one cup of the pasta water before draining.
In a food processor, combine the spinach, Parmesan cheese, cashew nuts, walnuts, fresh basil leaves, and garlic cloves. Pulse until the ingredients are finely chopped.
Add the lemon juice and slowly pour in the extra-virgin olive oil while the processor is running until the mixture becomes smooth. If the pesto is too thick, you can add a little bit of the reserved pasta water to reach the desired consistency.
Season with pepper to taste but no salt as the crumbled feta at the end will add a salt to the final dish.
In a large bowl, toss the cooked and drained pasta with the spinach pesto. If the mixture seems dry, add a bit more of the reserved pasta water until the pasta is well coated and the sauce has a creamy consistency.
Add the drained and roughly chopped sun-dried tomatoes, drained mini mozzarella balls and crumbled feta.
Give the salad a good mix, serve immediately, garnished with extra Parmesan cheese and fresh basil leaves if desired.