Preheat the oven to 425°F (220°C). Line a baking sheet with parchment paper and set it aside.
Prepare the vegetables: Wash and peel the veggies. Cut the tomatoes, carrots, bell pepper, onion, and zucchinis into appropriate sizes. Cube the sweet potato. Wrap the garlic bulbs in foil, season them with salt, pepper, and a little olive oil, and close the foil.
Season the vegetables: Place all the prepared vegetables (including the garlic bulb) onto the prepared baking sheet. Drizzle with olive oil, then sprinkle the basil, Italian seasoning, oregano, smoked paprika, cumin, chili flakes, salt, and black pepper over the veggies. Toss to coat evenly.
Roast the vegetables: Place the sheet in the preheated oven and roast for 40-45 minutes. Stir the vegetables halfway through to ensure they cook evenly. The vegetables should be tender and slightly caramelized when done.
Blend the soup: Once roasted, transfer the vegetables to a food processor or high-speed blender. Allow the garlic to cool slightly before squeezing out the roasted cloves. Add the boiling water and blend until smooth. You can add more water if you'd like a thinner consistency.
Add milk and adjust seasonings: Pour in the milk (or coconut milk for a vegan option) and blend again until well combined. Taste and adjust the seasoning with more salt, pepper, or spices if desired.
Serve: Pour the soup into bowls. Garnish with fresh basil leaves and heavy cream a sprinkle of black pepper. If the soup needs reheating, transfer it to a pot and bring it to a gentle boil over medium heat, stirring occasionally.
Optional: Serve with a side of toasted bread for a complete meal.