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.
While the steak is resting, toast or grill bread, if desired.
Assemble
Slice steak. Add steak, sauce, lettuce, peppers, and any other toppings to your sandwich.