Prepare the grill for two-zone (or direct/indirect grilling) method with lump charcoal. (While the grill is coming to temperature is a great time to make the chimichurri.)
Starting with the fat cap side, carefully remove excess fatty layers so the fat cap is about 1/4 inch thick. Then flip the roast over and remove any silver skin or pockets of fat that are on the underside of the roast.
Make X marks across the fat cap. This will not only allow the rub to get into the fat layer, it also helps when grilling the skewers as the fat renders and falls into the fire.
Slice the roast into about 2-inches thick slices aiming to keep each slice even. You will likely get five steaks.
Fold the individual steak in half, with the fat cap facing out. Then slowly skewer so the Picanha Steak is shaped like a U and the skewer has gone through both folds. Having large thick gauge skewers helps. Place three of the steak cuts per skewer trying to keep the similar sizes on each skewer. The end cuts will be smaller and we typically make sure the smaller cuts are on one skewer as they will cook through first.
Place the skewers over direct heat and close the lid. After 4 minutes flip the skewer, close the lid, and grill the other side over direct heat.
After 4 additional minutes (or your desired sear), move the Picanha to the indirect side and close the lid again. Continue grilling on indirect until the internal temperature of the skewers reaches 125 degrees F for rare, or your desired finishing temperature. It is highly likely the smaller of the two skewers will be done first, so remove them at separate times as they come to the desired internal temperature.
Remove skewers from the grill when they reach the desired internal temperature and let them rest for 10 minutes.
Holding the skewer in one hand and over a wooden cutting board, thinly slice the steak off the skewers and onto the cutting board. Serve the skewers with a dollop of the chimichurri sauce.
For more details on the process and additional photos see above.