Preheat oven to 450°F. Line two large shallow baking pans with parchment paper or foil. Spread tomatoes, onions, poblano halves, jalapeño halves, and garlic on prepared pans. Sprinkle with vinegar. Roast, uncovered, 30 minutes or until poblanos and onions are slightly charred. Cool slightly.
Meanwhile, in a 6-quart pot combine the next eight ingredients (through cumin). Bring to boiling; reduce heat. Cover and simmer 25 minutes or until squash is tender, stirring occasionally.
Transfer roasted vegetables, in batches, to a blender. Cover and blend until smooth. Transfer to pot. Bring to boiling; reduce heat. Cover and simmer 15 minutes, stirring occasionally.
Season with salt and black pepper. Serve chili topped with pepitas, scallions, and cilantro.