Add celery, carrot, and onion to a 6 quart slow cooker. Season the steaks with salt and pepper and place on top of the vegetables.
In a medium bowl, combine the diced tomatoes, beef broth, tomato paste, soy sauce, garlic, oregano. Pour over the steaks.
Cover and cook on low for 6-8 hours or on high for 3-4 hours or until steaks are fork tender.
Serve over riced or mashed cauliflower.
Notes
The sauce can be thickened if desired. Whisk 1 ½ tablespoons cornstarch with 1 ½ tablespoons water. Stir into the sauce cover and cook for an additional 15 minutes.