Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper.
Toss the chopped carrots, zucchini, onion, and garlic with olive oil on the prepared baking sheet. Season with salt and pepper.
Roast the vegetables for 25-30 minutes, stirring halfway through, until they're tender and lightly caramelized.
Transfer the roasted vegetables to a large pot and add the broth, thyme, and cumin.
Bring to a simmer and cook for 10 minutes to let the flavors meld.
Using an immersion blender (or transferring to a regular blender in batches), blend until smooth.
Stir in the cream if using, and adjust seasoning to taste.
Serve hot, garnished with a drizzle of cream and fresh thyme if desired.