Drain the tofu. Chop the onion finely, put into a heatproof container with the margarine, cover with plastic wrap and microwave for 2.5 minutes.
Mix the meat and salt together well in a large bowl. Add the mashed tofu, cooled down microwaved onion and egg, and mix everything together.
Divide into 4 portions. Form into oval shaped patties while pressing out any air pockets. Make a shallow well in the middle of each patty.
Heat up a frying pan over high heat. Add the patties and brown. Flip them over, brown the other side, then turn the heat down to low.
Add 1 tablespoon of water to the pan, cover with a lid and steam-cook.
Put the tomato sauce in a small pan with a little herb salt, and simmer it down a bit.
When the hamburgers are cooked, top with the sliced cheese. Put the lid back on and heat through until the cheese melts.
Put some sauce on the serving plates, add the hamburgers, and garnish with chopped parsley or basil.