Remove the meat from the refrigerator one hour ahead of time. This optional step will take the chill off for more even cooking and juicier meat.
Preheat your grill or oven to 400°F. When hot, oil the grill grates.
In a blender or food processor, add the olive oil, onion, garlic and salt. Process for 5-10 seconds or until you get a coarse, paste-like consistency. Set aside.
Place the picanha on a work surface. Score the fat side about a half-inch deep using a butcher's knife. Then cut vertically from the fat down into strips about 1 1/2 inches wide.
Rub the pieces of meat generously on all sides with the garlic mixture.
Fold one piece into a horseshoe and skewer it to hold the shape. Add second and third pieces onto the same skewer. Repeat for additional skewers as needed to use up the beef. Let it sit for up to 15 minutes to marinate.
Using kitchen tongs, place the picanha steaks on the grill and close the lid. Cook for 4-6 minutes per side or until they reach your desired doneness: 120°F for rare, 130°F for medium rare or 140°F for medium. Always check doneness by inserting an instant-read thermometer into the thickest part.
Remove the picanha to a serving plater and tent with foil to keep warm. Let it rest for 5 minutes undisturbed so the juices can redistribute through the meat.
Slice against the grain and garnish with optional black pepper and minced parsley to serve.