Set a dry skillet over medium heat. Lay in the unpeeled garlic cloves and chiles. Roast, turning frequently, until soft and blotchy brown in spots, about 10 minutes for the chiles and 15 minutes for the garlic. Cool until handleable, then slip the skins off the garlic, pull stems off the chiles and roughly chop (no need to remove the seeds). Place in a food processor along with the cilantro (about 1 cup if packed), parsley (about 1 cup if packed), oil and 2 generous teaspoons salt. Process until nearly smooth (it will be pasty). Scrape into a storage container and refrigerate until serving time.
Pour the fresh lime juice over the scallops, cover and refrigerate for 1 to 1 1/2 hours, stirring every few minutes. When the scallops are as “done” as you like—break one open to see if it looks as cooked as you like (I like them still pink on the inside), drain off all but about 1/4 cup of the lime juice. Stir in 1/2 cup of the herb mixture, cucumber and avocado. Taste and season with more salt if you think necessary. Serve on lettuce leaf-lined plates or martini glasses. You’re ready to serve.