Heat a non-stick pan over medium heat. Once hot, add in the oil. Then sauté the pepper and onion until soft. Add in the chopped beef, butter, and steak seasoning; sauté for 3-4 minutes; season with salt and pepper to taste.
Top with cheese and melt. Portion the meat onto the bread.
Add the broth, thyme, and kitchen bouquet to the pan. Quickly bring to a boil while scraping up any leftover bits on the bottom of the pan. Add the cornstarch mixture a little at a time to lightly thicken the liquid. Season with salt and pepper to taste if needed.
Cut the sandwich in half and serve with au jus and pickles.