Spray a 9''x13'' baking dish with cooking spray or coat with oil.
Cut zucchini in half lengthwise and, using a spoon, scoop out the seeds and flesh, leaving about a 1/4 inch thick shell. Set the seeds and flesh aside on a cutting board.
Brush the zucchini shells with olive oil. Bake for 10 minutes, cut side up, in prepared baking dish. Remove from the oven and set aside.
Heat a skillet over medium heat.
Dice the reserved zucchini flesh and add to a bowl with the diced onions, tomato, tomato paste, minced garlic and all spices.
Add the ground beef to the skillet and cook until it starts to brown, about 5 minutes. Add the zucchini mixture to the pan and continue to cook until meat has cooked through, stirring often, an additional 5 minutes.
Fill each zucchini shell with about 1/3 cup of filling and return to the oven for 20 minutes.