Place kidney beans in medium bowl. Pour enough water over to cover beans by 3 inches. Let stand overnight. Drain.
Sauté chorizo in heavy large pot over medium heat until cooked through and fat is rendered, about 10 minutes. Transfer chorizo to paper towels; drain, leaving 2 tablespoons drippings in pot. Add onion and garlic; sauté until tender, about 6 minutes. Add 3 cups water, broth and beans; bring to boil. Reduce heat; cover. Simmer until beans are tender, 1 hour.
Add squash to soup. Cover; simmer until tender, about 15 minutes. Stir in bell peppers, corn and chorizo; simmer uncovered about 10 minutes longer.
Meanwhile, set aside 2 tablespoons pepitas for garnish. Blend remaining pepitas in blender until finely ground. Stir ground pepitas into soup. Season with salt and pepper. Sprinkle with reserved pepitas and serve.