Brush oil on the scallions, tomatillos and zucchini, then sprinkle them with salt and place over the direct heat of the grill. Cook, rotating or flipping occasionally, until everything chars and the tomatillos soften a bit, about 5 minutes.
Blend and chill soup: Combine the scallions, tomatillos and zucchini in a blender, along with the yogurt, basil, cucumber, garlic, lemon juice and a nice pinch of salt. Blend until smooth. If the consistency is too thick, add a handful of crushed ice and blend; this should fix it! Taste and season with salt, then taste again. Refrigerate at least four hours or up to overnight.
Serve. Mix the yogurt and honey in a small bowl. Serve the soup in bowls and drizzle with the yogurt mixture, and a shake or two of the hot sauce.