Heat the oil in a large pan. Add the onions and garlic and cook over low heat, stirring occasionally, for about 5 minutes until softened. Add the zucchini and cook, stirring frequently, for 2-3 minutes.
Add the tomatoes and bouillon to the pan and bring to a boil. Add the pasta, bring back to a boil, reduce the heat, and cover. Simmer for 5 minutes.
Skin and bone the fish, then cut it into c
hunks. Add to the pan with the basil or oregano and lemon rind and simmer gently for 5 minutes or until the fish is opaque and flakes easily (take care not to overcook it) and the pasta is tender, but still firm to the bite.
Blend the cornstarch with the water to a smooth paste and stir into the stew. Cook gently for 2 minutes, stirring occasionally, until thickened. Season with salt and pepper to taste.
Ladle the stew into 4 warmed soup bowls. Garnish with basil or oregano sprigs and serve immediately.