Preheat oven to 350F. In a large bowl combine bread crumbs, egg, half of the garlic, half of the rosemary, and the black pepper. Add ground beef; mix well. Shape meat mixture into 1-1/2-inch meatballs. Place meatballs in a foil-lined 15x10x1-inch baking pan. Bake about 15 minutes or until done in centers (160F). Set aside.
In a 5- to 6-quart Dutch oven heat oil over medium heat. Add carrots, sweet peppers, onion, and the remaining garlic; cook for 5 minutes, stirring occasionally. Add beef stock, the water, Great Northern beans, barley, and the remaining rosemary. Bring to boiling; reduce heat. Simmer, covered, about 15 minutes or until barley is tender.
Add meatballs to barley mixture; heat through. Stir in spinach just before serving.