How about on a PLT? Smoked provelone cooked crisp, lettuce & tomato, with horseradish mixed with ketchup ("cocktail sauce") or mustard ("Chinese mustard"). (this would be a replacement for the mayo version) on some wonderful multi-grain bread.
Vegie tempura or anything Japanese.
Put a dollup in a bowl of stew made with turnips, rutabegas, parsnips, potatoes & onions with kale.
I put it on baked potatoes or even french fries. (The grated in vinegar kind)
I don't think I can think of any vegetable that wouldn't be good with horseradish, it is kinda like tabasco or soy sauce, it goes with everything. You could even put it in some cakes and cookies.