Prepare the Horseradish Dressing:

Whisk together all of the ingredients in a small bowl until well combined.

Prepare the salad:

In a large bowl, drizzle the oil over the cherry tomatoes, add the basil, and stir gently. Set aside.

Bring about 1 " of water to a boil in the bottom of a steamer. Put the beans in the steamer basket, place over the boiling water, cover and steam until crisp tender, 6 to 7 minutes. Refresh under cold running water and drain. Transfer to a second bowl. Add about half of the horseradish dressing and toss to coat.

Add the lettuce, radishes, and onion to the tomatoes. Season lightly with salt and pepper and toss. Arrange on a platter. Spoon the beans on top, and arrange the steak on top of the beans. Drizzle the remaining dressing over the steak and serve.