01 - Place cilantro, jalapeños, garlic, and green onions into a blender or food processor.
02 - Add lime juice, mayonnaise, Greek yogurt (or sour cream), Parmesan cheese, mustard, olive oil, kosher salt, and black pepper to the blender.
03 - Blend on high until completely smooth and creamy, scraping down the sides of the blender as needed to ensure even consistency.
04 - Taste the sauce and adjust seasoning as desired, adding more lime juice or salt to balance the flavors.
05 - Transfer to a serving bowl or airtight jar. Serve immediately alongside grilled meats, roasted vegetables, or sandwiches, or refrigerate covered for up to 3 days.