Season the chuck roast generously on all sides with salt, pepper, and onion powder.
In a large skillet over medium-high heat, melt butter and sear the roast for 3-4 minutes per side until browned, then transfer to slow cooker.
In the same skillet, add sliced onions and cook for 8-10 minutes, stirring frequently, until they begin to caramelize and turn golden brown.
Add garlic to the onions and cook for 1 minute until fragrant, then deglaze the pan with red wine, scraping up any browned bits.
Transfer the onion mixture to the slow cooker and add beef broth, Worcestershire sauce, thyme, and bay leaves.
Cover and cook on low for 8 hours or high for 5-6 hours until the meat is fork-tender and shreds easily.
Remove bay leaves, shred the roast if desired, and serve with the onion gravy, optionally topped with melted gruyere cheese.