Gazpacho is Spain’s culinary lifeblood, a refreshing puree of vegetables that blurs the distinction between soup and salad. Grilling adds a smoky dimension that transforms this warm-weather soup from the realm of refreshing to unforgettable. If you are using a food processor, puree the vegetables first, then add the liquids.
Step 1: Finely chop the scallion greens and set aside for garnish. Thread the scallion whites crosswise on a skewer and add the garlic cloves. Thread the onion quarters on a second skewer. Lightly brush the scallion whites, garlic, and onion quarters with about 1 tablespoon of the olive oil.
Step 2: Set up the grill for direct grilling and preheat to high.
Step 3: When ready to cook, brush and oil the grill grate. Place the skewered vegetables on the hot grate with the aluminum foil shield under the ends of the skewers. Grill, turning with tongs, until nicely browned, 4 to 8 minutes in all. Transfer the vegetables to a plate to cool. Add the bread slices to the grill grate and grill until darkly toasted, 1 to 2 minutes per side. Set the bread aside. Grill the toma- toes and bell peppers until the skins are nicely charred, about 8 to 12 minutes in all for the tomatoes, 16 to 20 minutes for the peppers. Transfer the tomatoes and bell peppers to a platter to cool. Using a paring knife, scrape the charred skins and burned bits off the tomatoes, onion, and bell peppers (don’t worry about removing every last bit). Core and seed the peppers.
Step 4: Cut the scallion whites, garlic, onion, toast, tomatoes, bell peppers, and cucumber into 1-inch pieces. Place the pieces in a blender or food processor, adding the tomatoes first, along with the mixed herbs, wine vinegar, and the remaining olive oil. Process to a smooth puree. Thin the gazpacho to pourable consistency with cold water as needed, and season with salt and black pepper to taste.
Step 5: The gazpacho can be served now, but it will taste even better if you chill it for an hour or so to allow the flavors to blend. Just before serving, taste for seasoning, adding more vinegar and/or salt as necessary. To serve, ladle the gazpacho into bowls and sprinkle the chopped scallion greens on top.