Dissolve the yeast and sugar in cool water. Make a well in the flour, sprinkle with salt and pour in the water. Knead a dough, cover it with plastic wrap and leave it for 15 min.
Cut the meat into bites and put them in heated oil. Once the meat is braised, add the chopped onions, mushrooms and season. Fry on low heat until ready, while stirring periodically.
Roll out a wide circle from the dough onto a floured counter. Peel the apple, cut it into crescents and arrange them in the circle. Sprinkle with thyme and put it in an oiled oven dish.
Bake in a preheated 392°F (200 °C) oven to a golden crisp. Take the flatbread out and put the cooked meat in its middle, along with some of the oil. Sprinkle with grated cheese and return to the oven for the cheese to melt.