Prepare the beef by seasoning it with salt and pepper, then dredging it in flour.
Heat vegetable oil in a large skillet over medium-high heat, then sear the steak on both sides until browned.
Remove the steak from the skillet and set it aside. Add onions and garlic to the skillet, sautéing until soft.
Stir in the diced tomatoes, beef broth, Worcestershire sauce, and thyme, bringing the mixture to a simmer.
Return the beef to the skillet, ensuring it's submerged in the sauce, then cover and reduce the heat.
Braised the steak for 1.5 to 2 hours, or until tender, checking occasionally.
Adjust seasonings as needed, and serve the Swiss steak with the sauce ladled over top.