Preheat your grill or cast-iron grill pan to medium-high heat to ensure a perfect, smoky sear.
Slice the sweet potato into half-inch rounds and trim the woody ends off the asparagus spears.
Season the flank steak evenly on both sides with the sea salt and black pepper.
Prepare the chimichurri by finely chopping the parsley and cilantro, then whisking them in a small bowl with minced garlic, red wine vinegar, dried oregano, red pepper flakes, and half of the olive oil.
Lightly brush the sweet potato rounds and asparagus with the remaining olive oil to prevent sticking.
Place the steak on the grill and cook for approximately 4 to 5 minutes per side for medium-rare, or until it reaches your desired doneness.
Add the sweet potato rounds to the grill at the same time as the steak, and add the asparagus during the last 4 minutes of cooking time.
Remove the steak from the grill and let it rest on a cutting board for at least 5 minutes to allow the juices to redistribute.
Slice the steak thinly against the grain and serve alongside the grilled vegetables, drizzling the fresh chimichurri generously over the meat.