Place the stemmed and rinsed tomatoes in a heavy saucepan with a tight-fitting lid. Add half the shallots, 1/2 tsp of salt, and 1 cup water. Cook over medium-high heat, keeping an ear to the pot. Soon you'll hear the tomatoes popping. Take a peek after a few minutes to make sure there's still sufficient moisture in the pot - you don't want the tomatoes to scorch. If the skins are slow to pop, add a few tablespoons of water. Once they release their juices, lower the heat and cook, still covered, for 25 minutes.

Run the tomatoes through a food mill. You'll have about 2 cups. Chill well, then salt to taste.

Just before serving, combine the remaining shallots in a bowl with the vinegar, chili (if using), oil, avocado, and herbs. Spoon the soup into small cups, top with the garnish, and serve.