1. Preheat oven to 500°.
2. Heat a large nonstick skillet over high heat; add onion. Coat onion with cooking spray; stir in 1/2 teaspoon seasoning blend. Sauté 11 to 12 minutes or until onion is tender and golden brown. While onion cooks, add 2 tablespoons water at a time; cook each time until liquid evaporates, scraping pan to loosen browned bits.
3. While onion cooks, combine broth and remaining 1 1/2 teaspoons seasoning blend in a medium saucepan; cook over medium heat until hot. Remove pan from heat; add beef, pushing beef down into liquid until covered. Let stand 5 minutes.
4. While beef stands, place hoagie rolls, cut sides up, on a baking sheet. Bake at 500° for 4 minutes or until bread is lightly toasted.
5. Remove beef from broth, allowing excess broth to drip back into pan; reserve broth. Arrange beef evenly over bottom halves of rolls; top evenly with onion, cheese slices, and remaining bread halves. Serve with warm broth for dipping.