2 tablespoons olive oil
1 small onion, grated
1/4 cup chopped fresh Italian parsley
1 large egg
3 tablespoons ketchup
3 garlic cloves, minced
1 teaspoon salt
1/4 teaspoon freshly ground black pepper
1/3 cup grated Pecorino Romano
1/4 cup dried plain bread crumbs
1 pound ground beef, preferably lean
2 zucchini, ends removed, halved lengthwise and crosswise
1 orange bell pepper, halved and seeded
1 red bell pepper, halved and seeded
1 green bell pepper, halved and seeded
1 1/2 cups marinara sauce
Preheat the oven to 400 degrees F.
Lightly drizzle the olive oil into a 13 by 9 by 2-inch baking dish.Whisk the onion, parsley, egg, ketchup, garlic, salt, and pepper in a large bowl to blend. Stir in the cheese and bread crumbs. Mix in the ground beef. Cover and refrigerate the beef mixture.
Using a melon baller or spoon, carefully scrape out the seeds and inner flesh from the zucchini, leaving 1/8-inch-thick shells. Be careful not to pierce through the skin. Fill the zucchini and pepper halves with the turkey mixture, dividing equally and mounding slightly. Arrange the stuffed vegetables in the baking dish. Pour the marinara sauce over the stuffed vegetables.
Bake uncovered until the vegetables are tender and beginning to brown and a thermometer inserted into the filling registers 165 degrees F, about 45 minutes. Transfer the stuffed vegetables to a platter and serve.