Melt shortening in a large Dutch oven over medium heat. Add roast, and brown roast on all sides; sprinkle with salt and pepper. Top meat with onion, green pepper, carrots, and potatoes. Cover and bake at 300° for 2 hours or until meat is tender.
Remove roast and vegetables to a serving platter; reserve pan drippings in Dutch oven. Combine flour and water; stir until smooth. Pour flour mixture into pan drippings. Cook over low heat, stirring constantly, until thickened and bubbly. Serve gravy with roast and vegetables.