01 - Preheat the oven to 325°F (163°C).
02 - Pat the beef chuck roast dry with paper towels and rub evenly with olive oil. In a small bowl, combine the kosher salt, black pepper, dried oregano, dried basil, garlic powder, and crushed red pepper flakes. Coat the roast thoroughly on all sides with the spice mixture.
03 - Heat a large Dutch oven or heavy oven-safe pot over medium-high heat. Place the seasoned roast in the pot and brown on all sides, approximately 2 to 3 minutes per side, until a deep crust forms.
04 - Remove the roast and set aside. In the same pot, add the sliced onion and minced garlic. Sauté for 2 to 3 minutes until softened and fragrant, scraping up any browned bits from the bottom of the pot.
05 - Pour in the beef broth, water, Worcestershire sauce, Italian seasoning, sliced green bell pepper, and fennel seeds. Stir well, bringing the liquid to a gentle simmer while deglazing the pot to release all caramelized fond.
06 - Return the seared roast to the pot, cover tightly with a lid, and transfer to the preheated oven. Braise for 2.5 to 3 hours, or until the beef is fork-tender and easily pulls apart.
07 - Remove the roast from the pot and let it rest for 15 minutes. Strain the cooking liquid through a fine-mesh strainer into a bowl, discarding the solids. Skim off any excess fat from the surface of the au jus.
08 - Thinly slice the rested beef against the grain using a sharp knife or meat slicer for ultra-thin cuts. Return the sliced beef to the strained au jus and simmer gently for 5 to 10 minutes so the meat absorbs the flavorful broth.
09 - Pile the au jus-soaked beef generously onto split rolls. Ladle extra au jus over the top and finish with giardiniera and roasted sweet peppers to taste. Serve immediately with additional au jus on the side for dipping.