Method:
Preheat oven to 425°F. Have ready 2 large nonstick baking sheets or regular baking sheets lined with parchment paper. Place peppers and eggplant on one sheet, squash and zucchini on second sheet. Roast vegetables, turning them once halfway through cooking and switching trays top to bottom and front to back, until browned, 30 to 40 minutes. Cool vegetables slightly, then coarsely chop.
Meanwhile, combine broth and olives in a blender and blend until smooth. Pour into a heavy pot and add tomatoes, onion, garlic and pepper flakes. Bring to a boil, lower heat, cover, and simmer until tomatoes are very soft, about 20 minutes.
Add roasted vegetables and marjoram to pot; cover and simmer, stirring once or twice, until flavors blend, about 10 minutes. Stir in parsley and vinegar; cook 5 minutes more.