Prepare the Marinade: In a mixing bowl, combine soy sauce, minced garlic, freshly grated ginger, brown sugar, sesame oil, and red pepper flakes. Whisk until well blended and allow to rest.

Sear the Roast: Heat a skillet over medium-high heat, sear the chuck roast for 4-5 minutes on each side until browned, then transfer to a slow cooker.

Add the Vegetables: In the same skillet, sauté carrots, onions, and mushrooms for 3-4 minutes, then layer around the beef in the slow cooker.

Pour the Marinade: Pour the marinade over the roast and vegetables, cover, and cook on low for 8 hours.

Check for Doneness: Ensure the meat is fork-tender and the internal temperature reaches 190°F (88°C).

Let it Rest: Allow the roast to rest for 15-20 minutes covered loosely with foil.

Serve and Garnish: Slice or shred, serve over rice or in tacos, and garnish with chopped green onions.