Pungent blue cheese and beef complement each other. To achieve that great flavor combo, these steaks are briefly marinated in a blue cheese dressing before grilling.
In small bowl, whisk vinegar, mustard, honey, garlic, salt, pepper and thyme. Gradually whisk in oil until well blended. Stir in 1/2 cup crumbled cheese, mashing slightly. Remove 2/3 cup dressing to plastic food-storage bag. Add the shell steaks; seal. Turn to coat; marinate 10 minutes.
Prepare outdoor grill with hot coals, heat gas grill to hot, or heat oven broiler.
In bowl, gently toss zucchini and 2 tablespoons of remaining dressing.
Remove steaks from marinade. Grill or broil 2 minutes. Flip over. Top each with 1-1/2 tablespoons remaining crumbled cheese. Grill 2 minutes for medium-rare. Remove to platter.
Grill or broil zucchini slices until tender, about 2 minutes per side.
In bowl, toss together greens, zucchini, onion, remaining dressing and any remaining crumbled cheese. Serve salad alongside grilled steaks.