In a medium bowl, combine parsley, basil, capers, garlic, anchovy paste, and red pepper flakes. Drizzle in olive oil and red wine vinegar. Mix well and let rest for at least 5 minutes.

In a large mixing bowl, add cannellini beans, cherry tomatoes, Castelvetrano olives, and red onion. Sprinkle with kosher salt to taste, then toss gently.

Drizzle the salsa verde over the bean mixture and fold everything together. Add parmesan shavings and mix lightly.

If using, top with tuna, then serve immediately or refrigerate for up to 3 days.