Arrange tomatoes on a baking sheet; drizzle with 2 tablespoons olive oil.
Add garlic and 3 sprigs chopped thyme; toss. Season with salt and black pepper.
Bake in preheated oven until very tender and browned, about 2 hours.
Heat remaining 2 tablespoons olive oil in a Dutch oven or heavy pot over medium heat; cook and stir onion, celery, and zucchini until tender, about 5 minutes. Stir in red pepper flakes, paprika, and curry powder. Season with salt and black pepper and add remaining 3 sprigs chopped thyme. Stir in roasted tomatoes along with any liquid from the baking sheet. Cook and stir for 5 more minutes; pour chicken broth into tomato mixture. Simmer for 20 minutes.
Blend with an emersion blender until desired consistency. Stir in cream and basil before serving.