Tip:To adapt a slow-cooker recipe to a conventional oven, follow these guidelines: add more liquid, to accommodate for greater evaporation; bring the dish to a boil over high heat in a Dutch oven, then cover the pot and put in a 350°F oven. Plan on the dish taking roughly half the time to cook in the oven as it would in the slow cooker.
Put 1⁄4 cup of the pomegranate molasses, the mustard, garlic, coriander, salt, and pepper in the slow cooker and use a wooden spoon to mix well. Add the meat and turn to coat with the mixture (use your fingers to smear the mixture all over the meat).
Heat 2 Tbs. of the oil in a 10-inch, heavy sauté pan over medium heat. When hot, add the onions and cook, stirring occasionally, until golden brown, limp, and sweet, about 20 minutes (discard any strips of red onion skin that separate from the flesh). Pour the onions on top of the meat.
Add the remaining tablespoon of oil, plus the tomato paste and flour to the pan. Stir until no white flour is visible, about 1 minute. Remove the pan from the heat and carefully add the wine; return the pan to the heat, raise the heat to high, and simmer for about 2 minutes, whisking into a smooth, thick sauce. Add the remaining 2 Tbs. pomegranate molasses, the tomatoes with juices, stock, orange juice, and honey, and use a potato masher to gently mash the tomatoes. Boil until smooth and relatively thick, about 4 minutes, then pour over the meat-onion mixture.
Cover and cook on low until tender, about 8 hours. Carefully transfer the meat to a cutting board, and let rest for about 10 minutes. With a large shallow spoon or ladle, skim the fat off the top of the cooking juices. Cut the meat against the grain into roughly 1⁄3-inch-thick slices, mix it back into the sauce, and serve, garnished with the pomegranate seeds.