Make Stock - If using a food processor to mince vegetables, add carrot, celery, onion, and red bell pepper. Pulse to break everything into tiny pieces. Otherwise, finally chop vegetables by hand. Don't go to far or it'll become an unappetizing paste. Heat the oil in a large pot over medium heat, add the minced vegetables and cook until soft, around 10-12 minutes. Stir in tomato paste and cook another 2 minutes. Turn heat up to high. Add zucchini, garlic, and diced tomatoes. Brown for 2-3 minutes, stirring. Pour in fish broth and saffron and bring to a boil.