Heavily season both sides of the roast(s) with salt and pepper. Sear both sides and all ends of the roast(s) in a hot pan. Place roast(s) into a large baking dish. (13x9-inch pan)
Cook roast(s) in the pan covered with foil at 300˚F for 4 hours. (Do NOT add water to pan, the roast(s) will release their own juices.)
Once meat is tender, drain and reserve juices, and shred the meat. Skim the fat off the top of the juices. Add juices back into the shredded meat and set aside.
In a LARGE sauté pan, melt shortening/coconut oil and add the onions. Cook for 5 minutes or until soft and translucent. Add flour and stir with onions for 1 minute. Mix in green chiles, salsa verde, garlic powder, salt, and cumin. Cook until thick. Add meat mixture into the onion mixture and heat thoroughly.
Fill tortillas with about ⅓ to ½ cup meat each and fold burrito style.
Heat oil in a large pot. Place chimichangas carefully seam side down into the oil and fry both sides until golden brown (approximately 45 seconds each side.) Allow to drain on a paper towel lined plate. Serve with sour cream, cheese, and hot sauce as desired.