Discard stems and gills (dark brown layers) from mushrooms.
Season steaks with 1/2 teaspoon salt and pepper. Place steaks on grill (or in grill pan); grill 3-4 minutes on each side or until steak is 145 degrees F. Remove steaks from grill; let stand 5 minutes before slicing.
Combine zucchini, tomatoes, portabellas, oil, and remaining 1/2 teaspoon salt. Place vegetables on grill; grill 2-3 minutes on each side or until tender and grill marks begin to show.
Remove vegetables from grill; cut into bite-size pieces. Slice steaks.
Divide salad greens onto 4 serving plates; top with vegetables and steak. Drizzle each salad with balsamic glaze and salad dressing. Serve.