Cook pasta according to package directions.

Meanwhile, place peas, spinach, basil, Parmesan, olive oil, walnuts, garlic and salt and pepper in a blender or food processor.

Two minutes before pasta is done, ladle out 1/2 cup hot pasta cooking water and add to blender. Pulse until smooth, scraping sides and adding additional pasta water by the tablespoon, if needed.

When pasta is done, drain lightly and return to pot. Add sauce and toss to coat. Season to taste with salt and pepper. Serve immediately with additional Parmesan cheese and tomatoes, if desired.