Heat the oil in a stockpot over medium heat. Combine the onion, celery, cinnamon, nutmeg, and cloves in the hot oil and cook and stir 3 to 5 minutes. Crumble the vegetable bouillon into the onion mixture; stir. Slowly add the boiling water to the mixture while stirring. When the water returns to a boil, add the carrots and sweet potato; season with salt; cover and cook until the potato and carrots are tender, 20 to 25 minutes; remove from heat. Scrape the flesh from the baked squash and pumpkin and add to the soup. Allow soup to cool for 15 minutes.