Prepare the Chuck Roast: Place the chuck roast in a slow cooker or oven-safe pot.

Mix the Marinade: Combine soy sauce, hoisin sauce, honey, rice vinegar, brown sugar, minced garlic, minced ginger, sesame oil, and optional chili flakes in a bowl. Whisk until smooth.

Coat the Roast: Pour the marinade over the chuck roast, ensuring it's fully coated. Let marinate for about 15 minutes if time allows.

Set Cooking Temperature: Slow cook on Low for 6-8 hours or preheat oven to 325°F (160°C) and cook covered.

Check for Doneness: Ensure the roast is fork-tender after cooking. Cook longer if needed.

Keep the Roast Warm: Remove roast, cover with foil to rest while preparing the glaze.

Prepare the Glaze: Simmer remaining sauce in a saucepan, scraping brown bits until reduced.

Thicken the Sauce: Stir in cornstarch slurry into the sauce until glossy.

Serve the Roast: Slice against the grain and drizzle the glaze over each slice.

Add the Finishing Touches: Garnish with sesame seeds and green onions.