Sort and wash beans; place in a large Dutch oven. Cover with water 2 inches above beans; let soak overnight. Drain and rinse beans; set aside.
Melt shortening in a medium skillet; add lamb, and sauté over medium heat until browned.
Combine beans, lamb, salt, pepper, and onion with water to cover in a large Dutch oven. Bring to a boil; reduce heat. Cover and simmer 1 hour. Add celery and tomatoes; cook 30 minutes or until lamb is tender.
Remove lamb and vegetables with a slotted spoon, reserving pan liquid in Dutch oven. Set lamb and vegetables aside, and keep warm.
Combine flour and water, blending until smooth. Add to reserved pan liquid, blending well. Cook over medium heat, stirring frequently, until mixture is thickened. Stir in lamb and vegetables, mixing well. Serve immediately.