Heat an outdoor or indoor grill to medium-high; oil the grill grate.
Season steak with salt and pepper. Grill steak for four to five minutes a side or until meat reaches desired doneness (medium-rare is very pink in the center; medium is light pink in the center; well-done is brown throughout). Remove from the grill and slice into 1/4-inch pieces.
Place Fresh Express® Spring Mix in a large bowl. Add tomatoes and onions. Drizzle with dressing and toss to coat.
Divide salad evenly onto four plates; top with steak.