- In a small bowl, combine garlic, herbs, and olive oil. Pour over steak, evenly coating all sides, and set aside in refrigerator to marinate for at least 3 hours or overnight.
- Prepare a grill for medium heat. Grill onion and jalapeño until well-browned and softened. Peel and de-seed jalapeño, then dice together with onion until both are jammy in consistency. In a bowl, combine onion-jalapeño mixture with remaining ingredients. Set aside.
- Rub steak liberally with salt and pepper and let stand at room temperature for 1 hour before cooking. Prepare a grill for high heat. Sear all sides of meat evenly, moving and turning regularly for even browning. Move away from direct heat and roast slowly until internal temperature reaches 125 degrees (for medium-rare to medium), about 10 to 20 minutes. Remove from heat and set aside to rest for 10 to 15 minutes before slicing thinly against the grain. Garnish with garden herb and charred onion chimichurri.