1. Preheat the oven to 350°F (175°C).
2. Heat the oil in a large skillet over medium heat; add the onion and sauté until starting to soften, about 5 minutes, stirring occasionally. Add the meat, 1 teaspoon salt, and the pepper; turn the heat up to high and cook until the meat is fully browned and the onion is tender, about 5 minutes, stirring occasionally and using a wooden spoon to break up the meat. Add the garlic and tomato and cook 5 minutes more.
3. Transfer the meat mixture to a medium-sized casserole dish along with the potato and marrow squash (or zucchini or eggplant); stir to combine.
4. Whisk together the tomato paste, pomegranate molasses, water, and remaining salt in a small bowl; drizzle on top of the casserole.
5. Cover the casserole dish and bake until the veggies are tender, about 1 hour to 1 hour, 15 minutes.
6. Stir in the fresh parsley leaves and serve with Arabic flatbread or Rice with Toasted Vermicelli Noodles.