Trim fat from meat. If necessary, cut roast to fit into a 3-1/2- or 4-quart slow cooker. In a large skillet brown meat on all sides in hot oil. Drain fat. Transfer meat to cooker; add water. Sprinkle roast with 2 teaspoons of fresh dillweed or 3/4 teaspoon of dried dillweed, the salt, and pepper.
Cover and cook on low-heat setting for 10 to 12 hours or on high-heat setting for 5 to 6 hours. Transfer meat to a serving plater, reserving juices; cover roast with foil to keep warm. Pour cooking juices into a large measuring cup; skim fat. Measure 1 cup reserved juices.
For sauce, in a small saucepan stir together yogurt and flour. Stir in the 1 cup reserved cooking juices and remaining dillweed. Cook and stir until thickened and bubbly. Cook and stir for 1 minute more. Pour some of the sauce over meat; pass remaining sauce. If desired, serve with pasta. Makes 6 servings.