Remove the top from the pepper, and remove the seeds and membranes if you prefer a milder sauce. Chop it into four pieces and put it into the food processor.
Add the lime juice, avocado, cilantro, salt, and cumin, and process until it's mostly smooth, scraping down the sides as needed.
Add the sour cream and continue to process until no large chunks remain. Refrigerate any unused sauce.
Macros per serving (2 tablespoons): 45 calories, 1 gram net carbs, 1 gram protein, 4 grams fat.