Heat the olive oil over medium heat in a large skillet. Generously season the meat with salt and pepper. When the oil in the pan begins to smoke, add the meat to the pan. Sear the meat on all sides, cooking until just browned.
2 tablespoons vegetable oil, kosher salt and black pepper, 2 1/2 pounds rump roast
While the meat is searing, add the condensed French onion soup, beef broth, Worcestershire sauce, dried onion flakes, garlic cloves, bay leaves, and dried oregano to the slow cooker. Then add the meat.
Cook on low for 6 to 8 hours. Remove the meat from the crockpot and let stand for 10 minutes. Slice the beef as thin as possible, or shred it.
Add the slices to the hoagie rolls. Top with a small amount of the cooking liquid from the crockpot. Add more of the cooking liquid to small cups for dipping.
Optional: Put slices of the beef with a ladle of the liquid into a skillet. Bring the liquid to a simmer, then turn off the heat. Add cheese to the meat and allow it to melt. Then transfer the meat and cheese to the hoagie rolls.
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Notes
Please note that the nutritional values are based on making six sandwiches, using a roll that is 176 calories, and no cheese.