Remove Cover from the package of beef and cook beef in the microwave on full power for one minute. Remove beef roast from package. Reserve 1/3 cup of the au jus. Set aside. In a large skillet, cook onion and garlic and hot oil over medium-high heat until tender. Stir in beef.
Lightly coat the inside of a 3 1/2 or 4 quart slow cooker with cooking spray. Add beef mixture to cooker. Stir in the reserved 1/3 cup au jus, cheese dip, sweet peppers, mushrooms, pepperoncini, Worcestershire sauce, and black pepper.
Cover and cook on high heat setting for 1 to 2 hours. Serve at once or keep warm, covered, on warm setting or low heat setting for up to two hours. Serve with hoagie planks. Makes 20 servings.
Hoagie planks: preheat broiler. Split five hoagie buns and place, cut side up, on a baking sheet. Spread with about 1/4 cup softened butter and sprinkled with 1/2 teaspoon dried Italian seasoning, crushed. Broil 4 to 5 inches from the heat for 2 to 3 minutes or until lightly toasted. To serve, cut one half diagonally into pieces.