Place the pieces of beef in your slow cooker. Sprinkle with the flour, salt and pepper. Toss with your hands to coat the meat with the flour. (For extra flavor I used a couple of teaspoons of Montreal Steak Seasoning, instead of salt and pepper.)
Add the onion, pepper, tomatoes, mushrooms and soy sauce.
Cover and cook on LOW for 7 to 8 hours, until the beef and vegetables are tender.