- With the rack in the middle position, preheat the oven to 425°F (220°C). Line a baking sheet with parchment paper.
- In a large pot over medium heat, soften the onions in the butter until translucent. Add the remaining vegetables and continue cooking for 2 minutes. Add the broth and milk. Bring to a boil and simmer, covered, for 30 minutes or until the vegetables are tender. Season with salt and pepper.
- In a blender, purée the soup until very smooth. Add the sesame oil. Adjust the seasoning and keep warm.
- Meanwhile, place the fish on the prepared baking sheet and drizzle with the oil. Season with salt and pepper.
- Roast for 8 minutes or until flaky. With a fork, break up the fish into large chunks.
- In a small bowl, combine the radishes, chives and lemon juice.
- Divide the fish pieces among six shallow bowls. Pour the hot soup over the fish. Garnish with the radish mixture and drizzle with sesame oil, if desired.