1. Place steak in large zip-top plastic bag; pour marinade over steak. Seal bag, pressing out excess air; massage in bag to coat and refrigerate at least 2 or up to 12 hours.
2. Prepare outdoor grill for direct grilling over medium-high heat. In food processor, pulse garlic, arugula, cilantro, parsley, vinegar, 1 teaspoon salt, 1/2 teaspoon black pepper, cayenne pepper and oregano until slightly chunky, scraping down bowl occasionally; slowly add 1/2 cup oil through feed tube and process until smooth. Transfer to small bowl; cover and refrigerate. Makes about 1 cup chimichurri.
3. Coat onion slices with remaining 1 tablespoon oil, and sprinkle with remaining 1/2 teaspoon salt and pepper. Remove steak from marinade; discard marinade. Place steak and onion slices on hot grill rack; cover and cook 8 minutes or until internal temperature of steak reaches 135° for medium-rare, turning once. Transfer steak to cutting board; tent with aluminum foil and let stand 10 minutes. (Internal temperature will rise to 145° upon standing.) Thinly slice steak against the grain; separate onion slices into rings. Makes about 1 cup onion.
4. Serve steak and onion topped with 1/2 cup chimichurri garnished with cilantro and/or parsley, if desired.

Chef Tip(s): Serve steak with white rice, Spanish rice or cilantro lime rice. Use remaining chimichurri on eggs, grain bowls and veggies.