In large nonmetal dish or resealable food-storage plastic bag, place steak. Add 1/4 cup of the vinaigrette dressing; turn to coat. Cover dish or seal bag; refrigerate at least 4 hours or overnight to marinate.
When ready to grill, heat gas or charcoal grill. When grill is heated, remove steak from marinade; discard marinade. Place steak on gas grill over medium heat or on charcoal grill over medium coals; cover grill. Cook 10 to 12 minutes, turning once, until desired doneness. Cut steak diagonally across grain into thin slices.
In large bowl, toss spinach, strawberries, onions and remaining 1/2 cup vinaigrette dressing to mix.
Divide spinach mixture evenly onto serving plates. Top each with steak slices; sprinkle with almonds.