Preheat oven to 375 degrees F. Cook the pasta according to package directions. Drain and return to hot pan. Add spinach; toss to combine. Spoon into a 2-quart casserole; set aside.
In a small saucepan, combine vegetable broth, onion, and garlic. Bring to boiling; reduce heat. Simmer, uncovered, about 5 minutes or until onion is tender. Remove from heat and set aside.
Place cashews in a food processor. Cover and process until finely ground. Add half of the water; blend until smooth. Add onion mixture, beans, lemon juice, mustard, salt, and pepper. Cover and process until smooth. Transfer to a medium bowl and stir in the remaining water. Stir bean mixture into pasta mixture in casserole. Sprinkle with bread crumbs.
Bake, uncovered, about 30 minutes or until crumbs are toasted. Let stand for 10 minutes before serving.