Fit a mini food processor with the s blade. Add the garlic cloves, rosemary and thyme. Process until finely chopped. Scrape the sides and add the olive oil. Pulse to combine.
Trim the skirt steak of any excess fat and cut it in half horizontally or into thirds for easier grilling. Put the steak pieces into a large re-sealable plastic bag and add the garlic herb mixture. Mix the marinade around to evenly coat the steak, and let marinate at room temperature for 30-60 minutes, or refrigerate for up to 24 hours.
Preheat a grill or grill pan to medium-high. If the steak has been refrigerated, let it sit at room temperature for at least 15 minutes. Remove the skirt steak from the marinade, scraping off most of the garlic, and pat dry. Season with salt and pepper.
Place the steak on the grill and cook, covered, until browned with grill marks on the bottom, about 3-4 minutes. Turn over and cook until browned on the other side, about 3-4 minutes longer for medium rare.
Transfer to a cutting board and tent lightly with foil. Let rest 10 minutes. Thinly slice the meat against the grain and serve with Salsa Verde.