Generously season both sides of roast with salt and pepper. Put roast and about 1 cup of water in a slow cooker. Cook on high 4-5 hours or on low 8-9 hours.
Remove roast from the slow cooker and shred.
Sautee diced onions in olive oil. Add juice from the bottom of the slow cooker, beef broth, garlic, Worcestershire sauce, rosemary, thyme and salt. Let simmer for about 5 minutes.
Pour the au jus in a blender. Blend until the onions are pureed. Add Kitchen Bouquet and flour and blend again.
Return shredded roast to the slow cooker. Pour au jus sauce over roast. Let it cook on low until ready to serve.
Sautee sliced onions in butter.
Butter Hoagie Buns and broil until toasted.
Drain roast with a slotted spoon and put on the bottom of hoagie bun. Layer sautéed onion over roast. Cover the top of the hoagie bun with sliced cheese. Return sandwiches to the broiler just until cheese is melted.
Ladle au jus into little mugs for serving and serve next to sandwiches.