Start by preparing the chimichurri sauce. In a mixing bowl, combine parsley, oregano, minced garlic, red wine vinegar, olive oil, red pepper flakes, salt, and black pepper. Mix thoroughly until all ingredients are well incorporated.
Let the chimichurri sauce sit for at least 10 minutes to let the flavors meld. This can be prepared ahead and stored in the refrigerator.
Preheat your grill or grill pan to a medium-high heat.
While the grill is heating up, brush both sides of the tuna steaks with olive oil and season with salt and pepper.
Once the grill is hot, place the tuna steaks on it.
Grill for about 3-4 minutes on each side or until the desired doneness is achieved.
Remove the tuna from the grill and let it rest for a couple of minutes.
Serve the grilled tuna steaks drizzled with the prepared chimichurri sauce.