Step 1

Preheat oven to 400°. Brush a baking sheet with 1 Tbsp. oil. Place squash halves, cut side down, on baking sheet and tuck a garlic clove under the hollow of each half. Roast until squash is tender all the way through, about 45 minutes. When cool, scoop out squash flesh and reserve, along with roasted garlic. Discard squash skins. DO AHEAD: Squash and garlic can be roasted 1 day ahead. Cover and chill.

Step 2

Heat remaining 1 Tbsp. oil in a large heavy pot over medium heat. Add onion; cook until softened, about 5 minutes. Stir in ginger, 2 tsp. salt, and turmeric. Cook until fragrant, about 30 seconds. Add roasted squash and garlic cloves and stir to coat. Add tomatoes and chicken broth; bring to a boil. Reduce heat and simmer to allow flavors to meld, about 20 minutes.

Step 3

Using an immersion blender, purée soup until smooth. (Alternatively, allow soup to cool slightly and purée in small batches in a blender.) Season with salt and pepper.