I have not had the tomato salad there, but have you tried looking for just German recipes? We are Austrian & German and my grandma, mom and I all make variations of this salad. My grandpa's rule of thumb was to always add onion and lots of pepper! (ahhh memories). Sorry I can't be of more help. But maybe you could do a Google search.
Was it made with vinegar?
Anyway, again sorry I could not be more help!