1. Combine the mushrooms, carrots, celery, onion, garlic, black pepper, and red wine in a large zip-top plastic bag. Add the steak, press out all the air, and seal the bag. Refrigerate for 8 hours or overnight.

2. Heat a grill for direct high heat. Pull the meat out of the marinade and brush off any herbs or vegetables. Pat the meat completely dry with paper towels and brush all over with grapeseed oil. Aggressively season both sides of the steak with salt.

3. Scrape the grill clean and coat it with oil. Set the steak over direct heat on the grill with the grain at a 45-degree angle to the grates; grill for 5 minutes. Rotate the steak 90 degrees and grill for 3 minutes. Flip the steak so the grain is again at a 45-degree angle to the grates; grill for 5 minutes more. Rotate 90 degrees and cook to rare (120º to 125ºF internal temperature), about 2 minutes longer. Transfer the steak to a plate and let the meat rest for 5 minutes. Slice the steak very thinly across the grain. Serve with the chimichurri sauce.