Heat 1 tablespoon oil in a large, non-stick frying pan over high heat. Add the silver beet, salt and pepper and cook, stirring frequently, for 3-4 minutes or until just wilted. Drain well on absorbent paper and set aside. Wipe the frying pan clean and heat 1 tablespoon oil over high heat. add the onion and garlic and cook, stirring frequently, for 2-3 minutes or until golden. Add the mince and harissa and cook, breaking up any lumps with a wooden spoon, for 8-10 minutes or until golden and cooked through. Remove from the heat and stir through the salt and pepper, parsley and sumac. Set aside to cool completely.
To make the dough, place the yeast, sugar and water in a bowl and mix to combine. Set aside in a warm place for 5 minutes or until bubbles appear on the surface. Place the flour and salt in a bowl and make a well in the centre. Add the yeast mixture and mix together with well-floured hands to form a dough. Turn out onto a lightly floured surface and knead for 3-4 minutes or until smooth and elastic. Place in a lightly greased, large bowl under a clean, damp cloth and set aside in a warm place for 15-20 minutes or until doubled in size.
Divide the dough into 4 pieces and roll out on a lightly floured surface to 25 x 35cm rectangles. Place the silver beet, mince mixture, feta and havarti (or mozzarella) cheese onto one side of the rectangles, leaving a 2cm border. Brush to remove any excess flour. Fold the dough over to enclose the filling and press the edges to seal.
Heat a large, non-stick frying pan over medium heat. Brush the gozleme with oil and cook, in batches, for 3-4 minutes each side or until golden and cooked through. Serve with yoghurt, lemon wedges and a sprinkle of sumac.