Preheat the oven at 400°F. In a large skillet, cook the breakfast sausage, making small crumbles. Drain and set aside. Cut the ends off zucchini. Cut zucchini in half lengthwise; with a spoon, scoop out pulp, leaving 1/2-in. shells.
In same skillet, heat olive oil and cook onion over medium heat until tender. Remove from the heat. While the skillet is warm, add sausage, 1/2 cup cheese, crushed tomatoes, chopped parsley, dill, cooked rice, tomatoes, salt and pepper; mix well. Let sit for 5 minutes. Spoon the mixture into the zucchini shells. Place in a greased 13x9-in. baking dish. Sprinkle with remaining mozzarella cheese.
Bake, uncovered, at 400°F for 30-35 minutes or until zucchini is tender. Serve warm and, if desired, garnish with chopped parsley or dill.