Combine all ingredients except chives in a 6-qt. slow cooker. Cover and cook on low until peas are tender but still retain their shape, about 8 hours.
Remove turkey leg and discard bay leaf. Stir soup to break apart peas and thicken soup. When turkey leg is cool enough to handle, pull meat into large shreds, discarding skin, bone, and gristle. Garnish soup with turkey meat and chives.