Again i have found a vegetarian solution to a danish smørrebrøds classic. http://maanebarnet.org/2014/12/27/makrelfrisalat/
The mackerel is replaced with young green jackfruit from a can (i imagine that you can also make fried fish, pulled pork or other dishes with this).
I did not use sugar, but added dried thyme
next time i will replace the yoghurt with homemade tofumayo :
12 oz firm silken tofu (drained and padded dry) = 340g
1 tsp apple cider vinegar
1 tsp Dijon mustard
1 Tbsp lemon juice
1 tsp agave syrup or your choice of sweetener
1/2 tsp salt
1/2 tsp white or black ground pepper
1 Tbsp olive oil
Blend and taste if something needs to be added.
If you want to use the mayo for something besides the non-mackerel-salat you can play with adding different herbs such as garlic, chili, dill or chives.