1. In a food processor, pulse 1/3 of tomatoes at a time until finely chopped. Pour into a bowl.
2. In a small saucepan over medium heat, combine vinegar, lime leaves, and lemongrass. Bring to a simmer, then remove from heat and stir into tomato mixture. Chill about 2 hours to blend flavors. Press mixture through a coarse strainer into another bowl and discard contents of strainer.
3. Stir remaining ingredients into tomato mixture, adding Sriracha and fish sauce to taste. Chill until cold and flavors are blended, at least 30 minutes and as long as overnight.
Note: Nutritional analysis is per 1-cup serving.