Combine the broth, oregano, basil, garlic powder, red pepper flakes, Worcestershire and pepperoncini brine in a slow cooker.
Add the sautéed bell pepper and sliced pepperoncini. Cover and cook on high for 25 minutes to blend the broth.
Add the cooked roast beef, turn the slices in the liquid, cover and cook on low for 20 to 30 minutes until the meat reaches 165°F.
Split the rolls and toast the cut sides until lightly crisp.
Lift the beef and peppers with tongs, let excess liquid drip back into the cooker and fill the rolls. Serve a small cup of the hot jus beside each sandwich if desired.