Preheat oven to 400F and move the rack to the middle position.
Prep your carrots and squash. I sliced my carrots into approx. 1/4" thick slices and the squash into about 3/4" pieces so everything cooks fairly evenly.
Add the carrots and squash to a baking sheet and toss with 3 tablespoons olive oil, the balsamic vinegar, garlic powder, Italian seasoning, and salt & pepper. Roast for 35-45 minutes, or until the carrots and squash are nice and soft and lightly browned. It's a good idea to check how they're doing after about 25 minutes or so, and you can also give the veggies a flip/stir at this point if you wish.
When the veggies are about done roasting, heat the remaining tablespoon of olive oil over medium-high heat in a soup pot. Sauté until the onion is lightly browned (5-7 minutes).
Add the carrots and squash, vegetable broth, and ground cumin to the pot. Increase heat to high and once it starts to gently boil, reduce heat to medium-low and simmer for 5-10 minutes.
Take the pot off the heat and blend the soup in batches (I suggest waiting at least 10 minutes for the soup to cool first to make this safer). Once the soup is blended, season with extra salt & pepper and thin with some water if needed.