Cut beef chuck into 5-6 large chunks, about 2-3 inches across.
Season beef generously with kosher salt (approximately 2-3 tbsp or 30g) and let it sit for 15 minutes.
Heat olive oil in a large non-stick pan over medium-high heat. Sear the beef chunks for 5-10 minutes until browned on two sides.
Add beef to a slow cooker. I like to use my instant pot for this.
Deglaze the pan with a splash of water or stock, then pour it over the beef in the slow cooker.
Add stock, onion powder, garlic powder, oregano, basil, chili flakes, coriander, paprika, worcestershire, tomato paste, and beef bouillon to the slow cooker. Stir to combine. Slow cook on low for 8-10 hours or until tender.
Remove the beef from the slow cooker and shred it into smaller pieces, but not fully shredded.
Heat olive oil in a pan over medium-high heat and refry the shredded beef for 4-5 minutes until it's a littlel crispy around the edges.
Add 2-3 cups of beef jus to the pan and reduce by half.
To assemble the sandwiches, slightly crisp up the Italian rolls in the oven for 5 minutes.
Layer giardiniera, shredded refried Italian beef, and concentrated jus on the rolls.
Wrap the sandwiches tightly with parchment paper.
GIARDINIERA
Break down cauliflower into small florets. Small dice celery, carrots, bell pepper, onion. Thinly slice chiles and press or mince garlic. Combine in a bowl.
In a pot, bring vinegar, water, and salt to a boil. Add in the vegetables, remove from heat, cover, and let them cool in the brine. Once cool, marinate for at least 8 hours in the refrigerator.
The next day, drain the pickling liquid and top the vegetables with canola oil and olive oil.