Whisk together the olive oil, chopped parsley, lemon juice, and garlic. Pour over the tuna steaks.
Preheat a grill over medium heat or place a grill pan over medium heat. Once hot, place the tuna steaks and grill for 5 minutes, flip, and cook for another 2-3 minutes, or until the tuna reaches an internal temperature of 125°F for medium rare. (See the notes for other levels of doneness).
Remove the tuna steaks from the grill, rest for a minute, then serve immediately.
Notes
Tuna steaks are best served medium-rare (125- 130°F). If you prefer it even rarer, look for 115F. For medium, aim for 135°F, and for well done, look for anything above 145°F. TO STORE: Let the leftovers cool completely, then store them in an airtight container in the fridge for 2-3 days. TO FREEZE: Store the fully cooled steaks in a freezer bag and freeze for 3 months. Let them thaw fully overnight before reheating. TO REHEAT: Reheat leftovers in the microwave for 20-30 seconds or in a skillet on the stovetop over medium heat until warm.