01 - Place the cilantro leaves, seeded jalapeño peppers, garlic cloves, and chopped green onions into a blender or food processor.
02 - Add the fresh lime juice, mayonnaise, Greek yogurt (or sour cream), grated Parmesan, mustard, olive oil, kosher salt, and black pepper to the blender.
03 - Process on high until the mixture is completely smooth and creamy, pausing to scrape down the sides of the blender as needed.
04 - Taste the sauce and adjust the seasoning, adding additional lime juice or salt to your preference.
05 - Transfer the finished sauce to a serving bowl or airtight jar. Serve immediately alongside grilled meats, roasted vegetables, or sandwiches. Alternatively, cover and refrigerate for up to 3 days.