Combine apple cider vinegar, ground mustard, and coriander seeds in a sauce pan.  Bring to a boil.  Cook until reduced by half and slightly syrupy. Remove from the heat.

Warm a small skillet on the stove.  Either use a non-stick pan or very lightly coat a stainless steel pan with olive oil (I use a paper towel to spread it around -  you don't want to introduce oil to the recipe, rather just trying to prevent the pan from sticking).  Once the pan is warm, toss in the red pepper, green onion, and garlic.  Keep the food moving - you don't want it to burn.  Only heat it for about 30 seconds to get the food warm - this will soften it and bring out some more flavor.  Remove the pan from the heat and place the contents into your mixing bowl.

While the cider is reducing, combine the remaining ingredients in a bowl, including the ingredients warmed in the pan.

Pour in the cider syrup mixture and stir the relish together.

Cover and refrigerate for at least 1 hour before serving.