Combine the first 10 ingredients in your slow cooker. Cover and cook on the low setting 4 hours, or until the vegetables are tender. Stir in the prawns, clams or mussels, and snapper. Cover and cook 10 to 15 minutes more, or until the prawns and fish are cooked, and the clams or mussels are open. Serve portions of the stew sprinkled with parsley.
Note: This recipe is designed for an oval-shaped slow cooker with a 5 litre or more capacity.