Pour olive oil in a large saucepan over medium-high heat.
Add carrots and onion, season with salt and pepper, and cook, stirring often, until carrots are softened, 15–20 minutes.
Stir in broth, coconut milk, and 2 Tbsp. chili sauce.
Bring to a boil, reduce heat, and simmer, stirring occasionally, until vegetables are very soft and liquid is slightly reduced, 40–45 minutes.
Let soup cool slightly, then purée in a blender until smooth.
Reheat in a clean saucepan, thinning with water to desired consistency; season with salt and pepper.
Divide soup among bowls, drizzle with chili sauce, and top with herbs or herb oil.