To make the chimichurri, pulse the garlic in a food processor until chopped.
Add the parsley, cilantro, jalapeno, lime juice, oil, oregano, salt, and water and process until blended.
Transfer 1/3 cup chimichurri to a large zip-close plastic bag; add the steak.
Squeeze out the air and seal the bag; turn to coat the steak.
Refrigerate, turning the bag occasionally, for 20-30 minutes or up to 4 hours.
Refrigerate the remaining sauce separately.
Spray the grill rack with non-stick spray; preheat the grill to medium-high or prepare a medium-hot fire.
Remove the steak from the marinade, discard the marinade, and place the steak on the grill rack.
Grill until an instant-read thermometer inserted into the side of the steak registers 145°F for medium, about 3-4 minutes on each side.
Place the steak on a cutting board, cover loosely with foil, and let rest 5 minutes.
Slice the meat on the diagonal into 20 slices.