Heat a large skillet over medium heat and add 1 tablespoon of the oil. Add the chopped onion and garlic and sauté until the onion is softened and fragrant. Transfer the mixture to a slow cooker.
In a large zip-top bag, combine the flour, garlic powder, and kosher salt. Add the cubed antelope, tossing lightly to coat. Shake off excess flour and set aside.
Add the remaining tablespoon of oil to the skillet. Working in batches, sear the antelope until golden brown on all sides. Transfer the browned meat to the slow cooker.
Carefully deglaze the skillet with the beef broth and red wine, scraping up all the browned bits from the bottom of the pan. Stir in the tomato paste, then pour the mixture over the meat in the slow cooker.
Add the bay leaf. Cover and cook on low for 4 hours.
Add the parsnips, carrots, potatoes, and red wine vinegar. Cover and continue cooking for 2–3 more hours, or until the meat is tender and the vegetables are soft.
Season with salt and pepper to taste, and garnish with fresh flat-leaf parsley.