Preheat oven to 400 and line a rimmed baking sheet with foil.
Heat grill to high and cook steak to your liking – about 3 minutes per side for medium rare. Let the steak rest under foil while you prepare the remaining ingredients.
Toss bread cubes with 1 tablespoon olive oil and a pinch each of salt and pepper. Place on prepared baking sheet and toast in the oven until golden, 5 to 10 minutes.
Slice steak into bite sized cubes and add to large bowl. Add bread cubes, tomato, cucumber and onion.
Shake remaining oil and vinegar together in a small jar with a pinch of salt and pepper. Pour over salad and toss. Add basil and toss again.
Let the salad sit for about 15 minutes so the flavors can combine and then serve.