Spoon soup into 4 to 5-quart slow cooker. Top with beef round steak, cutting into pieces if necessary to place in single layer. In small bowl, combine brown sugar, ketchup, chiles and garlic; mix well. Spread over beef. Top with tomatoes.
Cover; cook on Low setting for 8 to 9 hours.
About 10 minutes before serving, add bell pepper. Cover; cook an additional 10 minutes.
To serve, remove beef from slow cooker; place on cutting board. Cut into serving-sized pieces. Serve beef with sauce from slow cooker.