Place pork roast in a self-sealing plastic bag.

In a food processor, combine parsley, onion, and garlic.

Pulse until minced.

Add lemon juice, olive oil, dried oregano, red pepper flakes, salt, and black pepper to the food processor.

Process to blend into a chimichurri sauce.

Coat the pork roast with the chimichurri sauce in the plastic bag.

Seal the bag and refrigerate overnight to marinate.

Prepare a medium-hot fire in the grill.

Remove the pork roast from the marinade and discard the marinade.

Place the pork roast over a drip pan on the grill over indirect heat.

Close the grill cover.

Cook for about 1 hour (20 minutes per pound), until the internal temperature on a thermometer reads 145 degrees F.

Remove the roast from the heat.

Let it rest for about 10 minutes before slicing.

Garnish with lemon and lime slices.