Rub salt and pepper all over the roast, then rub on the flour. Heat olive oil in a large frying pan. Brown the roast about 3 minutes per side over medium-high heat.
Put sliced onions in the slow cooker pot. Set the roast over the onions in slow cooker.
Use a slotted spoon to scoop giardiniera from jar, measuring out mostly vegetables with just a small amount of the oil. Pour 1/2 cup of giardiniera on top of roast.
Sprinkle oregano, basil, fennel seeds, garlic powder, and crushed red pepper flakes over the roast.
Add chunk of butter on top of the roast.
Pour red wine into slow cooker pot with roast. Tuck the bay leaf and parmesan rind (if using) between roast and side of slow cooker pot.
Put the cover of the slow cooker in place.
Set to low heat and cook for 7 - 8 hours or until roast is very falling-apart tender and shreds easily with little to no resistance.
Remove bay leaf and parmesan rind. (Though I prefer to leave all the drippings, if you like, now would be the time to skim out a little of the accumulated fat, though some is needed to provide succulence to the meat.)
Use two forks to pull apart or shred the roast, stirring gently to coat the beef with fat and juices released during cooking.