Butter the slices of wheat bread & set aside.
Chop the spring onions finely.
Drain the tuna, pick to pieces w/ a fork & mix w/ the spring onion mess & set aside.
Chop the tomatoes & set aside.
Chop the mozzarella & set aside.
Whip the Greek yoghurt w/ the oils, the mustard, the dried herbs & add salt & pepper to taste.
Put 2 slices of bread (buttered side down) in a (non-stick) frying pan & heat it up. Add the dressing on top & distribute evenly. Add the tomato slices & half of the chopped mozzarella.
Add a lid & let it cook for 3-4 min. Carefully: always watch what happens to prevent the bread from burining.
As soon as the mozzarella is very smooth, add the tuna mess & the rest of the chopped mozzarella.
Put the remaining slices of bread on top (buttered side up).
Press together & flip over - carerfully. Put on the lid for another 3-4 min (or less).
Serve at once.