In a large nonstick skillet, heat oil over medium-high heat. Sprinkle ribs with peppercorns and salt. Cook, in batches, in hot oil about 5 minutes or until brown on all sides. Place ribs in a 6-quart slow cooker. Place onion slices on top of ribs. In a medium bowl, combine cranberry sauce, beef broth, rosemary and lemon juice. Pour over the ribs. Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting for 4 to 5 hours. Transfer ribs to a warm dish; cover to keep warm.