In large bowl, add venison, bread crumbs, tomato paste, Worchestershire sauce, mustard, onion powder, garlic powder, pepper, salt, onion, garlic, and parsley. Use your hands to combine well. Divide into 4 portions and make patties about 1/2 inch thick. Allow patties to rest for about 15 minutes
In large heavy-bottomed skillet, add avocado oil. When hot, add patties. Cook for 2-3 minutes. Flip carefully, and cook on other side for 3-4 minutes. Remove from skillet and set aside. Cover patties to keep warm
Add onions to skillet and cook for about 5 minutes, until translucent. Add mushrooms and continue to cook for about 3 minutes, until softened. Stir in thyme, garlic powder and flour or cornstarch, and cook for 1 minute. Add beef stock, scraping bottom of skillet to remove brown bits. Add Worchestershire sauce, and bring mixture to a boil.
When gravy begins to thicken, turn heat down and add butter. Stir well until butter melts into the gravy. Season with salt and pepper to taste.
Return patties to gravy. Spoon gravy over patties and cook for 5-7 minutes, until patties are no longer pink in the center.
Garnish with parsley. Serve with mashed potatoes, egg noodles, or root mashed vegetables