DO-AHEAD TIP: Grill and slice steak.
Preheat oven to 375 degrees.
On a parchment-lined sheet pan, toss together first 10 ingredients (vinegar through mushrooms); bake for 10 to 15 minutes or until veggies are tender.
In a large salad bowl, toss together roasted veggies, grilled steak slices and salad greens; add dressing then toss again and serve.