Set a large skillet over high heat. Once hot, add in the oil and the ground sirloin. Begin breaking it up with a wooden spoon and cook until no longer pink, about 5 to 8 minutes. Drain any excess grease if you have some accumulating. Stir in the onion and bell pepper and cook for another minute or 2 until softened.
Season with salt, pepper, paprika and ground mustard. Stir in the tomato paste and cook for about 30 seconds to develop the flavor of the paste. Stir in the flour and then add the stock, brown sugar and Worcestershire sauce. Reduce heat to a simmer and cook until the sauce has thickened, about 10 minutes.
To assemble the sandwiches, split the buns open and toast under a broiler. Pile the sloppy joes onto the bottom buns and drizzle with the warmed cheese whiz. Or you can place provolone cheese slices on the bottom bun and then pile the sloppy joe mixture on top. Place the top bun on and serve immediately. Enjoy!