In a bowl, combine all Marinade ingredients. Add steak and marinate for at least 30 minutes, or up to 2 hours.
Remove steak from marinade and pat dry. Chop steak into bite-sized pieces.
In a large skillet, melt 2 tbsp Butter over medium-high heat. Add chopped steak and cook until browned, about 5-7 minutes.
Add diced Onion, Green Bell Pepper, and Red Bell Pepper to the skillet with the steak. Cook until vegetables are tender-crisp, about 5 minutes.
To make the Gravy, melt 2 tbsp Butter in a separate saucepan over medium heat. Whisk in Flour and cook for 1-2 minutes to create a roux.
Gradually whisk in Beef Broth until smooth. Bring to a simmer, then stir in Worcestershire Sauce, Garlic Powder, and Black Pepper. Cook until thickened, about 5 minutes.
Pour Gravy over the steak and vegetables in the skillet. Stir to combine and heat through. Serve immediately.
