Slow cooking is at its best with this recipe. The beef slowly braises until it practically falls to shreds. Although great on sandwiches, it's also delicious over a baked potato topped with sour cream.
Arrange peppers on a baking sheet coated with cooking spray. Broil 6 minutes or until blackened in spots, turning occasionally.
Remove lid from a 6-quart Instant Pot®. Press [Sauté]; use [Adjust] to select "More" mode. When the word "Hot" appears, coat inner pot with cooking spray. Add beef; cook 5 minutes, turning to brown on all sides. Remove beef from pot.
Add peppers to pot; stir in vinegar and next 3 ingredients (through crushed red pepper). Stir in 1/4 teaspoon of the salt, black pepper, and chopped pepperoncini. Return beef to pot.
Close and lock the lid of the Instant Pot®. Turn the steam release handle to "Venting" position. Press [Slow Cook], and use [Adjust] to select "Less" mode. Press [-] or [+] to choose 8 hours cook time.
When time is up, remove beef from cooker; shred with 2 forks. Stir beef and remaining 1/4 teaspoon salt into cooking liquid. Divide beef mixture evenly among hamburger buns, using a slotted spoon. Serve any extra sauce for dipping.
Swap In A Snap! Use gluten-free hamburger buns to make this a gluten-free sandwich.