In a medium bowl, stir together the tomatoes, pepperoncini (plus about half the juice!), onion, water or broth, Italian dressing mix, oregano, and garlic powder.
Place the roast in a 5- to 6-quart slow cooker and pour that flavorful mixture right over the top. Cover and cook on low for 8-10 hours, until the meat is super tender and falls apart with a fork. (You can also do on high for 4-5 hours)
Once it’s done, take the roast out and let it cool slightly. Skim any fat off the top of the juices. Shred the beef with two forks, then pop it back into the slow cooker with all those juicy flavors. Let it warm through for a bit.
Serve piled high on toasted rolls with melty cheese, if you’re feelin’ it.