Step 1: Combine the tomatoes, cucumber, bell peppers, onion, and garlic in a large glass bowl.
Step 2: Just before serving, tightly cover the bowl with plastic wrap, leaving space for the rubber tube of the smoking gun. Light the gun according to the manufacturer’s directions and fill the bowl with smoke, pulling the plastic wrap tight to seal in the smoke. Let stand for 4 minutes. Uncover the bowl and stir in the smoke. Repeat once or twice or until the gazpacho is smoked to your taste.
Step 3: Place the vegetables in a food processor or blender and process to a smooth puree. Gradually add the oil and vinegar and enough ice water to make a pourable soup, about 1/2 cup. Add salt and pepper to taste, plus a few drops of vinegar if needed to balance the sweetness of the vegetables. The gazpacho can be made several hours ahead to this stage and refrigerated, but re-season it before serving.
Step 4: Pour the gazpacho into bowls or mugs. Sprinkle each with chopped chives and dig in.