Place ground beef in a large skillet. Cook and stir over medium-high heat until browned and crumbly, 5 to 7 minutes. Drain and discard grease. Transfer beef to a slow cooker.
Combine tomatoes, green pepper, water, tomato sauce, onions, rice, salt, chili powder, and Worcestershire sauce in the slow cooker. Stir thoroughly. Cover and cook on Low until rice is tender, 6 to 8 hours.