Prepare barbecue (medium-high heat). Whisk olive oil, vinegar, and tarragon in small bowl to blend. Mix in tomatoes and shallot. Season salad to taste with coarse salt and pepper. Let stand 15 minutes.
Sprinkle steak generously on both sides with coarse salt and pepper. Grill to desired doneness, about 6 minutes per side for medium-rare. Transfer to platter. Let stand 10 minutes.