1. Clean the parsley, and removed leaves from stems.
2. Chop garlic cloves and cut the lemons in half and discard the seeds, set aside.
3. In a food processor, blend parsley, olive oil, lemon juice, and garlic.
4. Transfer chimichurri sauce in a small bowl, season with salt, pepper, and red pepper flakes.
5. Refrigerate for 2 hours before cooking.
6. Preheat oven to bake at 350 degree.
7. Rinse tuna steaks and place in a Pyrex baking dish.
8. Pour 1/2 cup of chimichurri over tuna steaks.
9. Bake in preheated oven for 25-30 minutes.
10. Serve the tuna steak along with little of the chimichurri Sauce.