Pat the chuck roast dry with paper towels. Season all sides with salt and pepper.
Heat olive oil in a large skillet over medium-high heat. Sear the roast for 3-4 minutes per side until browned.
Place the roast in the bottom of the slow cooker.
Sprinkle the brown gravy mix and onion soup mix over the roast, and pour in the red wine vinegar.
Cover and cook on low for 8-10 hours, or on high for 5-6 hours, until the beef is very tender and shreds easily with a fork.
Remove the roast from the slow cooker and shred it with two forks. Return the beef to the slow cooker, stir into the gravy, and let it sit on warm for 10-15 minutes to absorb the flavors.
To serve, place mashed potatoes on a slice of garlic toast, spoon the shredded beef and gravy on top, and garnish with fresh parsley. Enjoy!
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Notes
Nutritional values are just for the beef and gravy and do not include the bread or mashed potatoes.