Mix together flour, salt, mustard, and pepper in a wide, shallow bowl. Add cube steaks to flour mixture; toss to coat completely.
Heat oil in a skillet over medium-high heat. Fry steaks in hot oil until golden brown, 2 to 3 minutes per side; transfer to a slow cooker, reserving drippings in the skillet.
Sauté onion and garlic in drippings in the skillet over medium heat until softened, 2 to 3 minutes; add to the slow cooker. Discard oil.
Stir together broth and tomato paste in a large bowl until paste is dissolved; add tomatoes, Worcestershire sauce, paprika, thyme, and oregano. Pour broth mixture over steaks in the slow cooker.
Cook on Low until meat is tender and falling apart, 6 to 8 hours.