Combine the garlic, jalapeno, vinegar, parsley, oregano and lime juice in a food processor. Add the olive oil and season with salt and pepper. Pulse until smooth and set aside at room temperature to allow the flavors to marry.
Reserve 1/2 cup of the chimichurri to serve and marinate the pork in the rest. Put the pork and marinade in a sealable plastic bag and set aside in the refrigerator for 30 minutes.
Outdoor grill cooking:
Preheat an outdoor charcoal grill.
Remove the pork from the marinade, wiping off any excess. Season both sides with a generous amount of salt and pepper. Drizzle with olive oil and place on the grill. Grill the pork on the hottest part of the barbecue for 4 minutes per side, until well charred. Allow the tenderloin to rest for about 5 minutes prior to slicing. Spoon some chimichurri over the meat, drizzle with lime juice, garnish with parsley, and serve with the remaining sauce at the table.
Remove pork from marinade, and pat dry with paper towel. Drizzle with olive oil and sprinkle with salt.
Heat oil in cast iron pan. Once hot, brown each side of pork for 1 minute. Place pan in oven at 400 for 25 minutes.
Remove from oven and tent with foil. Let rest for 10 minutes, before slicing. Serve with chimicurri sauce on top.