Whisk together the soy sauce, Worcestershire sauce, honey, garlic powder, red pepper flakes, black pepper, ginger, and 3 tablespoons of cornstarch. Set aside.
Add the beef, bell peppers and onion to the slow cooker, stir to mix.
Pour the sauce over the beef and veggies.
Cook on low for 6 hours.
In a small bowl, whisk 2 tablespoons of cornstarch with some hot water (about one cup). Pour into the slow cooker and stir.
Cook for an additional 15-20 minutes.
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