Place the chuck roast in the slow cooker crock. Sprinkle half of the au jus and gravy mix over the roast and gently rub it into the meat. Flip the roast and repeat with the remaining mix. Pour the water around the sides of the roast.
Cover and cook on low for 8 hours or on high for 6 hours. Remove the roast and place it on a cutting board. Discard excess fat and shred the beef using two forks. Reserve the broth for dipping.
In a large skillet over medium heat, melt the butter. Add the sliced onions and cook for 12–15 minutes, stirring occasionally, until soft and golden brown. Stir in thyme, salt, and pepper. Remove from heat and set aside.
Preheat oven to 350°F.Keeping the rolls intact, slice them horizontally to separate the tops and bottoms. Place the bottom half (cut-side up) into an 11×7-inch baking dish.
Layer with half of the provolone cheese, the shredded beef, caramelized onions, and remaining provolone cheese. Place the roll tops over the cheese.
In a small bowl, mix melted butter and dried onion soup mix. Brush evenly over the tops of the rolls (or pour carefully). Cover loosely with foil (make sure it doesn’t touch the rolls). Bake for 25 minutes, then uncover and bake an additional 5 minutes until the tops are golden brown.
Serve sliders warm with au jus on the side for dipping, Garnish with parsley if desired.