Preheat oven to 425 degrees F and line a large baking sheet with parchment paper.
Wash the skin of the squash and cut into 0.5" inch slices and then into half moons. Brush the squash with olive oil and sprinkle with salt and pepper. Transfer baking sheet to the oven and bake for 30-40 minutes, flipping halfway through cooking. Remove from the oven and allow to cool before peeling the skin off the flesh. Set aside.
Heat 2 tablespoons olive oil in a large stock pot or Dutch oven over medium-high heat. Add the onions and cook for 3-4 minutes, stirring often. Add the celery, carrots, and cauliflower, and sprinkle with salt and pepper. Stir well to combine. Cook for approximately 5-6 minutes, stirring frequently.
Add the garlic, ginger, and chopped red chili to the pot. Cook for 2-3 minutes, stirring continuously. Add the vegetable stock and bring to a low boil. Cover with a tight-fitting lid and reduce heat to low. Simmer until vegetables are soft (approximately 10 minutes).
Remove from heat and transfer the cooked squash to the pot.
Use a hand blender or high-speed blender to puree the soup until smooth and creamy. Add the coconut milk and stir to combine.
Transfer the miso paste to a small cup filled with warm water and whisk well to combine. Stir the miso into the soup and return the pot to medium-low heat. Heat just until warmed through but not boiling and season with salt and pepper, to taste.
Garnish soup with fresh cilantro, roasted butternut squash slices, sesame seeds, pumpkin seeds, coconut milk, and green onion. Enjoy!