Start by rinsing your flat-leaf parsley and kale leaves under cold water. Shake off any excess water and pat them dry with a paper towel.
In your food processor or blender, add the flat-leaf parsley, kale, fresh oregano leaves, and roughly chopped garlic.
Next, add the lime zest, fresh lime juice, white vinegar, salt, black pepper, and optional red pepper flakes for a little heat.
Pulse the mixture until the herbs and garlic are finely chopped but not completely pureed.
With the food processor running, slowly drizzle in the olive oil until the sauce is well combined.
Give your chimichurri a taste and adjust the seasoning if necessary.
Transfer the chimichurri sauce to a jar or container. It can be served immediately, but letting it sit for at least 30 minutes allows the flavors to meld beautifully.