Remove the flank steak from the fridge about 30 minutes before you plan on grilling and place it on a large rimmed baking sheet. In small bowl, combine two tablespoons olive oil and the garlic and rub into both sides of the steak and season both sides with salt and pepper.
Wash the potatoes, but leave the skin on. Place the potatoes in a saucepan and cover with water by 1 inch and add the salt. Bring to a boil and turn the heat down until the water just simmers, cover partially and cook for about 20 minutes or until potatoes are tender when pierced with a fork. Drain, let cool slightly and halve.
While the potatoes are cooking make the chimichurri. Place the garlic, red pepper flakes, cumin, 1/2 teaspoon salt, and sugar in a food processor. Process until the garlic is minced. Add the parsley and lemon juice and pulse into the parsley is finely chopped. While the machine is running, pour the 1/2 cup of oil through the feed tube and process until well blended. Set aside.
Grill the steak. Preheat your grill to high. Oil the grate and place the flank steak directly over the flames. Sear the steak on one side for about 4 minutes, turn and sear the other side for about 4 minutes or until your desired degree of doneness.
Transfer steak to a cutting board and let rest for 10 minutes and then slice across the grain.
To serve arrange to potatoes and steak on 4 plates and drizzle with the chimichurri sauce (you might have extra chimichurri sauce.)
This chimichurri sauce can used on roasted vegetables or also as a marinade!