1. Put the zucchini in a medium saucepan. Add enough water to cover and boil until tender (5 minutes).
2. Preheat oven to 350 degrees F. Prepare a baking dish with non-stick cooking spray.
3. Split the zucchini in half lengthwise and scoop out most of the pulp. Reserve pulp, chop, and set aside.
4. Heat the olive oil in a non-stick saucepan. Add the onion and saute over medium heat until tender (4-5 minutes). Add the zucchini pulp and remaining ingredients except the pine nuts and tomato sauce. Cover and simmer over low heat until rice is tender (15-20 minutes).
5. Toast the pine nuts in a small skillet over medium heat until fragrant (3-5 minutes). Stir them into the rice mixture.
6. Stuff the mixture into the zucchini shells. Arrange the zucchini on the prepared baking dish and pour the tomato sauce over and around the shells. Cover with foil and bake until heated through (25-30 minutes).