Over medium how heat, heat the olive oil in a large stock pot. Add the onion, garlic, cilantro, and tortilla squares, and sauté, stirring frequently, until the onion is soft. Stir in the cumin and cayenne, and sauté for 1 more minute. Add the pumpkin, diced tomatoes and their juices, vegetable broth, and salt. Stir to combine, and bing to a boil. Cover and reduce heat to low. Simmer for 1 hour, stirring occasionally.