Rinse the flat-leaf parsley, kale, and oregano leaves thoroughly under cold water to remove any grit. Pat them dry with a clean kitchen towel or use a salad spinner. Roughly chop the garlic cloves.
Using a citrus zester, carefully remove the zest from one lime, avoiding the white pith. Then, squeeze out the lime juice and set both aside.
Add the parsley, kale, oregano, garlic, lime zest, lime juice, white vinegar, salt, black pepper, and red pepper flakes (if using) into your food processor or blender. Pulse a few times to begin breaking down the herbs.
With the processor running on low, slowly drizzle in the olive oil to emulsify the sauce. Continue blending until the mixture reaches a slightly chunky but well combined consistency.
Taste your chimichurri and adjust seasoning as needed — add more salt, vinegar, or lime juice to brighten it up or more red pepper flakes for heat. Blend briefly again if you add anything.
Transfer the sauce to a clean jar or bowl. Use immediately or refrigerate for at least an hour to allow flavors to meld.