Toss the sliced steak with the cornstarch until it is all lightly coated.

In a large skillet over medium high heat add the oil.

When the oil is hot add the beef in a single layer and cook quickly just to brown the outside. You may have to do more than one batch.

Add the beef to the slow cooker.

Add the bell pepper and onion to the slow cooker.

To a small bowl combine the sugar, ketchup, hoisin, soy sauce, sweet chili sauce, vinegar, water and red pepper flakes.

Stir everything to combine.

Cook on low for 3 hours, stirring once or twice to prevent sticking.

Garnish with sesame seeds.

Serve over rice!