Cut 4 ounces mozzarella into thin strips; cut remaining cheese into cubes. Set aside.
Cook orzo in a large saucepan according to package directions; drain and transfer to a large bowl.
Melt butter with oil in saucepan over medium heat; add onion, and sauté until tender. Add celery, and sauté 5 minutes.
Stir in flour, and sauté 3 minutes; stir in broth and next 3 ingredients. Cook, stirring constantly, 5 minutes. Stir tomato mixture, cheese cubes, olives, and salt into orzo; spoon into a lightly greased shallow 3-quart baking dish. Arrange cheese strips on top.
Bake at 350° for 45 minutes or until slightly crisp.