Start by thoroughly washing your flat-leaf parsley and kale under cold water. Remove any thick stems, as you want to keep the leaves tender. Pat them dry with a clean kitchen towel or use a salad spinner.
In a food processor, combine the parsley, kale, fresh oregano leaves, chopped garlic, lime zest, lime juice, white vinegar, salt, black pepper, and red pepper flakes (if using).
Pulse the mixture in the food processor until the herbs are finely chopped but not pureed. You want to maintain some texture, so be careful not to over-process.
With the food processor running, slowly drizzle in the olive oil until the mixture is well combined and emulsified. Scrape down the sides as needed to ensure everything is mixed evenly.
Taste your Chimichurri sauce and adjust the seasoning as desired. You can add more salt, lime juice, or olive oil based on your preference.
Transfer the Chimichurri sauce to a storage container. Allow it to sit for at least 30 minutes to let the flavors meld before serving. Enjoy with grilled meats, roasted vegetables, or as a zesty salad dressing!
