If using active dry yeast, add the yeast and sugar to 1 cup lukewarm water. Stir to dissolve, and let stand for 10 minutes to allow the yeast to activate. If using instant yeast, you can skip this step.
In a large mixing bowl, add the all purpose flour and salt. Stir to combine. Add the yogurt and activated yeast mixture (or the instant yeast along with the sugar and water).
Mix together with a fork or wooden spoon until the mixture forms a soft, shaggy dough. Knead for 10 minutes, dusting your hands and the dough with a sprinkling of flour if needed (the dough will get a bit sticky as you knead it).
After kneading, let the dough rest for 5 minutes. Spread the semolina onto a large rimmed sheet pan.
Roll the dough out to a thickness of about 1/2 an inch. Cut out circles with a 3 inch round cutter. Re-roll any excess and form more muffins. You should get 12-16 muffins total. Slide the muffins around on the semolina to ensure they don't stick to the pan. Cover with a damp towel and let rise in a warm place for about an hour, until almost doubled in size.
Heat a flat griddle pan until hot and brush with oil. Add the muffins and reduce heat to medium. Cook for 12 minutes, six minutes on each side, until firm and golden brown. Turn only once.
The best way to break the muffins apart is with a fork, to make sure you get great nooks and crannies. Serve toasted with butter and jam.