Spray slow cooker with cooking spray or use a slow cooker liner. If you are using bacon you must first fry it in a skillet until it is almost crisp, put it on paper towels and set aside.
It is easiest to slice the beef if you place it in the freezer for thirty minutes beforehand or slice it before it is totally defrosted. Thinly slice the beef with a very sharp serrated knife.
In a resealable bag add flour with ½ teaspoon of pepper and the sliced beef. Shake around until meat is coated. Place meat in slow cooker.
Add bacon, sliced pepper, mushrooms, onion, garlic, broth, crushed red pepper flakes (if using), and onion soup mix. Stir to combine.
Cover and cook on low 5-7 hours, or high 3 hours. The thinner the beef is sliced the quicker the beef will cook.
Add hot sauce to taste.
At this point you can make some rice or prepare your pitas to be stuffed. If you have some crusty rolls heat your oven to toast them. I usually cut open the rolls and put them under the broiler until brown. Next place cheese on each half of the bun. Back under the broiler until cheese is melted and lightly brown.
Next spoon meat mixture onto one half of each bun. Serve sandwich warm.