1. Chop fish into small pieces. Heat oil and brown onion and garlic. Add fish, lower heat and cook, gently stirring, until fish turns white. Season with salt and pepper.
  2. Add tomatoes and tomato paste to fish, and gently blend. Simmer for 5 minutes and before serving add finely chopped parsley.
  3. Cook spaghetti as directed and drain. Mix ½ cup sauce mixture into pasta. Place in serving dish and cover with remaining fish and tomato sauce.