Start with the dough, as it takes the most time to prepare. For that, add all ingredients (flour, water, salt, yeast) for the dough into a kitchen aid machine and let it mix it for 25 minutes at low speed.
Bring the bowl to a warm place (e.g. the technical room), cover it with a wet line towel and let it rest there for 2 hours, better 4-5 hours (or if you are in a hurry for less, but at least 60 minutes)
Peel the onions and cut it in slim slices, and sweat the onion.
Add the smoked tofu (or whatever similar is available, minced soya works as well, then just add more smoked salt)
Taste the mixture with smoked salt until it clearly has some smoky taste.
Roll the dough with a bit of flour onto a baking tray (either a large rectangle or then two/three round ones)
Spread the vegan sour-creme on the dough (a bit more than tomato sauce of a pizza). Depending on the type of sour-creme you might need more, as some of them get too liquit and they sink into the dough.
Then add the onion/tofu mix from the pan over the sour-creme
Cover everything with some vegan cheese. If you do not have vegan cheese, you could also use the same cover that I describe in the lasagna, but I would leave there all the herb away)
Place it into the oven for 20-25 minutes at 200 degrees (This obviously varies also with the type of cheese and the sour-creme)
After baking you can give some parsley over the Zwiebelkuchen.