Grilled-Everything Salad

Ingredients

• 2 tablespoons prepared horseradish
• 3 tablespoons red wine vinegar
• 5 tablespoons extra-virgin olive oil
• 1 teaspoon kosher salt
• 1/2 teaspoon freshly ground pepper
• 1 10-ounce package (or 2 bunches) fresh spinach, stems removed
• 1 1/2 pounds grilled flank steak, thinly sliced (6 cups)
• 1 large onion, thickly sliced and grilled (3 cups)
• 3 carrots, thinly sliced and grilled (3 cups)
• 3 plum tomatoes, halved and grilled