Spray inside of slow cooker with non-stick cooking spray. Add steak to bottom of slow cooker.
Add diced tomatoes, garlic, chopped onion, green pepper and mushrooms
Cook for 6-8 hours on low heat or until meat is tender.
When done, if you want the sauce thicker, add 1-2 tsp of cornstarch mixed with cold water (to make a cornstarch slurry) and cook for 20 minutes on high.Or you can add a little tomato paste to thicken it!
Serve over rice (I use brown minute rice), cauliflower rice, mashed potatoes or egg noodles.