Add the parsley, fresh oregano, and garlic to a food processor and pulse several times to chop finely. Spoon the mixture into a bowl and stir in olive oil, vinegar, salt, pepper, and red pepper flakes. Taste and adjust seasonings if necessary.
Serve immediately or refrigerate. You can serve it chilled or room temperature. Store in an airtight container in the refrigerator for one week.
Steak
Set steak out at least 30 minutes before cooking to come to room temperature. Preheat grill 450 degrees.
Rub salt, pepper, and garlic into both sides of the steak.
Grill 3 to 4 minutes on the first side, season top side, and flip steak. Grill 3 to 4 minutes more or until the desired doneness. Transfer from the grill and allow to sit before slicing.
Resting gives the juices time to redistribute so they don't immediately run out when you cut into the steak.
While the steak is resting, toast or grill bread, if desired.
A little toasted texture makes the sandwich even better and helps the bread stand up to the chimichurri.
Assemble
Slice steak. Add steak, sauce, lettuce, peppers, and any other toppings to your sandwich.