Preheat oven to 350 degree F. Grease 4 individual au gratin or casserole dishes; set aside. Cook orzo according to package directions; drain. Stir in spinach. Divide evenly prepared dishes. Place a sweet pepper half, cut-side-up, in each dish. Set aside.
In a large skillet cook sausage, mushrooms, onion, and garlic until meat is no longer pink and onion is tender. Drain off fat. Stir 1 cup of the Italian cheese, ricotta, feta, bread crumbs, egg, and olives into mushroom-sausage mixture. Spoon mixture into pepper halves. Pour marinara sauce over stuffed peppers and orzo mixture.
Cover with foil. Bake for 45 minutes or until heated through. Uncover and sprinkle with remaining Italian cheese. Let stand 5 minutes before serving. Makes 4 servings.