Heat the oil in a large skillet over medium high heat. Add the cubed steak and Steakhouse Rub, turning until all sides are browned (beef will not be fully cooked), about 3-4 minutes. Remove to a plate and set aside. Do not rinse out the skillet.
Add the potatoes and cook for 11-15 minutes, or until they are soft when pierced with a fork.
Add the mushrooms, red bell peppers, onions and garlic. Continue to cook until starting to soften and mushrooms reduce by half, approximately 3-4 minutes. If the skillet is dry, add another 1 teaspoon vegetable oil.
Stir in the butter, Worcestershire sauce, dark brown sugar and Dijon mustard, tossing until the sauce is smooth. Return the steak to the skillet and toss to coat, cooking another 1-2 minutes before serving.
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