Place potatoes and onions in a 3 qt slow cooker. In a large skillet brown meat in oil on all sides. Place over potato mixture.
Pour off excess fat from skillet. Add hot water to drippings, stirring to loosen browned bits from pan. stir in paprika, salt, caraway seeds, tomato paste, and garlic. Pour into slow cooker. Cover and cook on low for 7 hours.
Add green peppers and tomatoes. Cover and cook 1 hour longer or until meat and vegetables are tender. With slotted spoon, transfer meat and vegetables to a large serving bowl, cover and keep warm.
Pour cooking juices into a small pan. Combine flour and cold water until smooth, gradually whisk into the pan. Bring to a boil, cook and stir for 2 min or until thickened. Remove from heat; whisk in sour cream. Stir into meat mixture.