Fry the onion until golden, add chopped mushrooms and cinnamon. When the mushrooms are browned, let them cool.
Roast the chopped walnuts and also let them cool.
Blanch the Swiss chard until it softens, drain the water, chop it and put it in a bowl. Add eggs, spices, buttermilk, walnuts, fried mushrooms and flour. Mix everything well and make sure the mixture is not too runny or too thick (adjust with extra flour or milk). Pour it on the baked crust and bake it in the oven on medium high, for half an hour. Serve with yogurt and green salad,