Place roast in slow cooker. Sprinkle dried thyme over roast. Add quartered onion (just place the pieces anywhere in the pot).
In a bowl whisk together soy sauce, garlic, bay leaf, pepper, beef stock, and water. Pour into slow cooker. Cover and cook on high 4 hours or on low 8 hours.
When ready to serve, drain juices from the slow cooker and transfer to a serving bowl. Discard onions and bay leaf.
Shred roast with 2 forks. Place shredded beef on sliced hoagie rolls. Top with sliced swiss cheese. Place open under broiler in the oven for about 3-5 minutes until cheese is melted. Serve with reserved juices from the roast.