Place ham bone in a slow cooker. Pour in enough water to cover. Cook on Low until you have a fragrant stock, 12 to 15 hours.
Place navy beans, cranberry beans, and wheat berries in a large container and cover with several inches of cool water; let soak, 8 hours to overnight. Drain.
Remove ham bone from stock. Add beans and wheat berries. Stir in celery salt, thyme, oregano, Worcestershire sauce, and black pepper. Cook on High until beans are tender yet firm to the bite, about 4 hours.
Stir lentils into the slow cooker. Cook on High until tender, about 1 hour. Season with salt and black pepper. Serve soup topped with diced tomatoes, avocado, and green onions.
