Zesty red wine marinade is the key for this super-tender and deeply flavored steak. The longer it marinates, the better.
Place steaks and marinade in a 2-gal. zip-top plastic freezer bag; seal bag, and turn to coat. Chill 2 to 12 hours.
Preheat grill to 400° to 450° (high) heat. Grill steak, covered with grill lid, 5 to 7 minutes on each side or to desired degree of doneness. Remove from grill, and let stand 10 minutes.
Heat oil in a skillet over medium-high heat; add tomatoes, and cook, stirring occasionally, 10 minutes or until seared. Season with salt and pepper.
Cut 1 flank steak thinly across the grain; serve with tomatoes, arugula, and sauce. (Reserve remaining steak for salad and sandwiches.)
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