Preheat the oven to 300 F and line a large rimmed baking sheet with parchment paper or a Silpat baking mat. Set aside.
Slice yellow tomatoes into 1/2" slices and place them on a prepared baking sheet. Leave room between slices to prevent over-crowding. Sprinkle with salt, pepper, and garlic powder.
Place baking sheet in preheated oven and roast for approximately 2 hours until the tomatoes are browned around the edges.
Wash and pat radishes dry before slicing them into thin pieces*. Place on a lined baking sheet and sprinkle with salt and black pepper, to taste. Place in the oven with the tomatoes, but be sure to check on them frequently because they will brown up much faster than the tomatoes. Roast until slightly browned and crisp. Remove from the oven and reserve to garnish the finished soup.
*TIP: For best result, use a Mandlone slicer for radishes to achieve even thickness.
Once the tomatoes are done roasting, remove them from the oven and cool slightly. Add roasted tomato slices to a high-powered blender or food processor, along with the stock, basil, onion, celery, garlic, cumin, coconut milk. Season with salt and black pepper to taste.
Blend on high until smooth and thoroughly combined. Taste and adjust seasonings as needed. If desired, add additional vegetable stock, 1 tablespoon at a time, and re-blend to achieve desired consistency.
To serve, top with roasted radishes and a sprig of fresh basil. Enjoy!