In a medium dutch oven, heat the olive oil over medium heat. Add the onion and celery and cook until the onion is softened, about 10 minutes. Add 2 cups water, the potatoes, tomatoes and clam juice; season with salt and pepper. Bring to a boil over high heat, about 5 minutes. Lower the heat and simmer, stirring occasionally, until the potatoes are cooked through, about 20 minutes.
Season the cod with salt and pepper and arrange on top of the chowder, ladling with some broth. Cover the pot and cook until the fish is opaque, 3 to 5 minutes. Using a slotted spatula, transfer the cod to 4 soup bowls. Stir the parsley into the chowder, season with salt and pepper, then ladle into the bowls.