In a small bowl combine cashews and enough boiling water to cover. Let stand, covered, 20 minutes; drain. Rinse and drain again. Meanwhile, cook pasta according to package directions, adding asparagus the last 3 minutes and spinach and peas the last 1 minute; drain.
In a small saucepan whisk together 1 1/4 cups water and flour until smooth (mixture may be a bit foamy). Cook and stir over medium heat just until bubbly.
For sauce, in a blender combine soaked cashews, flour mixture, and next five ingredients (through pepper). Cover and pulse several times, then blend 5 minutes or until smooth. If desired, stir in basil and/or parsley.
Transfer pasta mixture to a serving dish. Drizzle with sauce; toss to coat. Sprinkle with additional black pepper and, if desired, cheese.