Hello Grapestomp
I use Mustard quite often when cooking, dijon, Keen's hot, and Australian Hot Outback. Here's my favorite recipe you might want to try. I used this on Salmon, but it would work just as well with any grilled fish.
instead of Honey, I use Maple Syrop. mix about 4 parts maple syrop with 1 part dijon mustard and a dash of veggie oil( I use Extra Virgin Olive Oil, but regular oil would work as well. mix together with a whisk and use it as a glaze Grill the fish ( either gas or BBQ) on indirect heat. After the fish has been turned brush the glaze over the fillet. put as much or as little as you like.
the maple syrop/mustard glaze will caramalize slightly and gives the fish a beautiful golden yellow colour.