Explanation: I don't think this has much to do with normal mustard (sennep). My guess is that they are talking about italian "mostarda" - see link: http://italianfood.about.com/od/saucescondiments/a/aa121405....
I would suggest to write something like "sennepssyltede grøntsager" or even use the italian word "mostarda" (like "æblemostarda" in one example below).
The translation workplace 
peer agreement (net): +3
