Rinse parsley and cilantro under cold water, then pat dry. Remove thick stems, aiming for 1 cup of packed leaves.

Combine parsley, cilantro, and garlic in a food processor. Add oregano, red pepper flakes, salt, and black pepper. Pulse until finely chopped but chunky.

Pour in olive oil, red wine vinegar, and lemon juice into the processor. Blend again until just combined, keeping it chunky.

Taste and adjust seasoning with more salt, pepper, or vinegar as needed. Blend briefly to mix adjustments.

Transfer chimichurri to a bowl or airtight jar. Enjoy immediately or store in the fridge for up to one week.