To prepare the bell peppers and onions:

• Add 2 tablespoons of olive oil into a large skillet.
• Add the sliced and seeded bell peppers, along with the peeled and sliced onion.
• Cook over medium/high heat (stirring occasionally) for 7-10 minutes, or until the peppers are nicely soft and the onions are lightly caramelized. Set aside until ready to use.
• Caramelized onions and bell peppers may be made in advance and kept in the refrigerator for 4-5 days.
• Preheat oven to 375-degrees Fahrenheit (190 degrees Celsius).
• Rip and tear 6-7 brioche buns into bite-sized pieces, and lay them in a single layer on a baking sheet.
• Bake the bun pieces for 30 minutes to toast. Remove them from the oven and gently stir. Return them to the oven for an additional 15-20 minutes until they turn golden brown. Set aside to cool.
• Meanwhile, remove the sliced Italian beef from the container (reserving the gravy at the bottom of the container). Using a chef's knife or santoku, chop the Italian beef into bite-sized pieces. Set aside.
• In a large bowl, whisk together 4 eggs, salt, pepper, and the gravy remaining in the container (approximately 4 cups) until thoroughly combined.
• Spray a 13x9 baking dish with cooking spray and layer the toasted brioche bun pieces evenly into the bottom of the casserole dish.
• Top the layer of toasted brioche with the prepared chopped Italian beef, and then ladle the egg/gravy mixture evenly over the top of the beef.
• If using, layer the caramelized onions and green pepper strips over the beef and gravy mixture and top the entire savory bread pudding with an even thick layer of shredded mozzarella cheese.
• Top the casserole evenly with the garlic powder, dried basil, and dried oregano.
• Bake in a preheated 350-degree Fahrenheit oven (190 degrees Celsius) for 50-60 minutes, or until the center is set and the cheese is melted.
• Cool for at least 15 minutes before serving, and enjoy!