1. Place split peas, ham hocks, carrots, leeks, bay leaf, parsley and salt in slow cooker. Stir in 6 cups water, cover and cook on low until peas are tender and ham is falling off the bone, 6 to 8 hours. Remove ham hocks, shred meat and return to cooker to keep warm.
2. Preheat oven to 400ºF; line a rimmed baking sheet with foil. Sprinkle cheese over bread slices. Place on baking sheet and toast until cheese is melted and bubbling, 1 to 2 minutes. Ladle soup into bowls, top each with a cheese toast, and serve.