Purée one 16-ounce jar fire-roasted red peppers with their juices, 1 tablespoons Sherry vinegar, 1/2 teaspoon kosher salt, and 1/4 teaspoon black pepper in a blender on high speed until very smooth, about 1 minute. With motor running, gradually add 1/4 cup extra-virgin olive oil. Season to taste with salt, pepper, and more vinegar, if desired. DO AHEAD Soup can be made 1 day ahead. Cover; chill.
Divide soup among small cups or shot glasses. Garnish with parsley, olive oil, minced bell peppers, toasted coriander seeds, caper berries, feta, or minced hard-boiled egg.