Pat the tri-tip dry with a paper towel or clean cloth. Season the steak generously on both sides with salt and pepper. Place the meat on a plate. Cover loosely and place in the refrigerator for at least 2 hours.
Remove the meat from the refrigerator, place it on the counter, and allow it to come to room temperature, about 30 minutes.
Heat the grill to medium-high, 400°F
If the grill is not clean, use a wire grill brush to clean the grates. Use a grill brush to apply a thin layer of cooking oil on the grill grates.
Place the steak on the grill, fat side down, and allow it to cook for about 6 minutes. Then, flip the steak and cook for about 6-8 minutes on the other side, or until the steak reaches an internal temperature of 130°F for medium-rare and 140° for medium.
Take the steak off of the grill and allow it to rest for 5-10 minutes as the steak becomes even more tender and the flavors are sealed.
While the steak is resting, combine all of the ingredients for the Chimichurri sauce in a food processor or blender. Blend until slightly pureed, leaving just a bit of texture.
Slice the tri-tip against the grain and pour a generous amount of the chimichurri over the steak.