In a bowl, whisk together the sauce ingredients.
Sear Roast - For extra flavor, you can heat up 1-2 tablespoons of a high heat oil (like canola oil) in a large, heavy pan (like cast iron) and sear the roast on all sides over medium-high heat to brown the outside.
Place the chuck roast in a large slow cooker. Pour over sauce and flip chuck roast over a few times so it gets a little coated on all sides.
Cover slow cooker and cook on low for 7-8 hours. You can also cook on high for 4 hours, but I prefer low as it becomes more tender. The beef is done when it is tender and easily shreds with two forks.
Shred chuck roast with two forks and toss with some or all of the sauce in the slow cooker.
To thicken the sauce, you can mix the cornstarch with ¼ cup of water to make a slurry. Add to the sauce in the crockpot, increase heat to High, cover, and cook for 20-30 minutes to chicken the sauce.
Sprinkle with sesame seeds, green onions, and serve.
