1. Position a rack on the top level of the oven, about 4 inches from the broiler. Turn on the broiler. Line a rimmed backing sheet with aluminum foil. Place the tomato halves cut side down, the onion slices and the chiles on the baking sheet. Broil for 12 minutes until vegetables are a bit charred. Remove from oven and let cool to room temperature. 

2. In a food processor, combine the roasted vegetables and any juice from the pan with the vinegar, cilantro, mint, and salt. Pulse until the mixture is almost smooth. If necessary, add up to 1/4 cup of water to achieve a consistency similar to a think soup.