Preheat the oven to 375 degrees F.
Cut the zucchini in half lengthwise (stem to bottom). Using a teaspoon or melon baller, scoop out and discard the zucchini flesh and seeds, leaving a 1/2-inch of flesh attached to the skin. If the zucchini are wobbly, cut a thin slice off the bottom to make them stand up.
Heat the olive oil in a large skillet, and sauté the chopped onion until softened, about 5 minutes. Add the ground beef to the pan, and cook until starting to brown. When the meat is about half cooked, add the bell pepper along with the seasoning blend, salt and pepper. Stir and continue to cook until the meat is fully browned, breaking it into small pieces with your spoon or spatula.
Remove from the heat, and stir in the rice, tomato sauce, and Parmesan cheese.
Choose a baking dish that is just big enough to hold the zucchini, and lightly grease it. Stuff the zucchini with the beef mixture, and top with a little extra tomato sauce and a sprinkle of Parmesan.
Place the zucchini in the baking dish and roast, uncovered, for 20-30 minutes or until the shells are crisp-tender and the filling is hot. After about 20 minutes of baking, I poke the zucchini with a sharp knife, and if the knife doesn’t slide in fairly easily, I bake them for a few minutes more. At this point, I occasionally sprinkle the zucchini with some grated sharp cheddar or mozzarella cheese and bake 2 to 3 minutes more or until the cheese is melted.