"My favorite salmon recipe so far. The combination of flavors is unexpected but works so well! My family loves salmon, but to me, it always just tastes pretty much the same. This is a fabulous change. Works well broiled, too."
For sauce: Mix all ingredients in a small bowl, and season with salt and pepper. Cover and chill if making ahead.
For salmon: Prepare grill by oiling grates and heating to med-high. Whisk oil, horseradish, soy, garlic, salt and pepper in another small bowl. Brush all over salmon, and grill just until opaque in center, about 4 min each side. Cook time will vary depending on thickness. (If using skin-on fillets, just cook skin side down, without turning.) Transfer fish to serving platter and serve with sauce.