Heat a tablespoon of neutral oil (like avocado or canola) in a large pot or Dutch oven over medium heat. Add the chopped onion and sauté until softened and translucent, about 5-7 minutes.

Stir in the minced garlic and grated ginger, cooking for another minute until fragrant. Be careful not to burn the garlic.

Add the turmeric, cumin, coriander, and cayenne pepper. Stir well to coat the aromatics and cook for 30 seconds to bloom the spices.

Add the cubed sweet potatoes and rinsed red lentils to the pot. Pour in the vegetable broth. Bring the mixture to a boil, then reduce heat to a simmer.

Cover the pot and let it simmer for 20-25 minutes, or until the lentils are tender and the sweet potatoes are easily pierced with a fork. Stir occasionally to prevent sticking.

Carefully transfer about half of the soup to a blender (or use an immersion blender directly in the pot). Blend until smooth and creamy. Return the blended portion to the pot with the remaining chunky soup.

Stir in the full-fat coconut milk and lime juice. Heat through gently over low heat for about 5 minutes, but do not boil after adding the coconut milk. Season generously with salt and black pepper to taste.

Ladle the bisque into bowls. Garnish with fresh cilantro and toasted pepitas for added texture and freshness. Serve hot.