Make the chimichurri sauce in a blender or food processor. Combine 1 cup fresh parsley, 3 whole garlic cloves, 1/2 teaspoon salt, 1/4 teaspoon black pepper, 1/4 teaspoon crushed red pepper flakes, 1/4 teaspoon dried oregano, 1 tablespoon extra virgin olive oil, 1 1/2 teaspoons red wine vinegar, and 1 1/2 teaspoons lemon juice. Pulse on high and blend until pureed.
Slice 12 large hard boiled eggs in half lengthwise and remove the yolk. Put all the yolks in a small mixing bowl and all the whites on a platter.
Add 1/4 cup of the chimichurri sauce, 1/4 cup mayonnaise, 1/2 teaspoon saltand 1/2 teaspoon black pepper to the yolks. Use a fork to mix until well combined and fluffy.
Spoon filling into the centers of the whites or use a pastry piping bag to fill. Garnish with a sprinkling of chopped parsley, freshly cracked black pepper, or red pepper flakes, if desired.
Chill in the fridge until ready to serve. Serve cold.