Cut the squash into chunks and roast at 400F/200C until tender (approx 20-25min) then leave to cool slightly. Blend the cooked squash until it's a relatively smooth paste. (Note the squash can be cooked ahead of time and stored in the fridge overnight.)
To make the pizza dough, put the flours, yeast, salt and sugar in a large bowl and mix together. Make a slight well in the middle and add the oil, yogurt and water and carefully mix together into a dough. It will be slightly wet and sticky. Tip the dough out onto a floured surface and knead for about 5 minutes, stretching the dough away from you with the back of your hand, folding the stretched part over on top of the rest of the dough, turning 90 degrees then repeating. Add a little more flour as you go, if needed. After around 5min it should stop feeling sticky. Clean out the mixing bowl, lightly oil it then form the dough into a ball and put it in the bowl. Cover with cling film/plastic wrap and leave it to rest somewhere warm for about an hour, possibly more, until it doubles in size.
When ready to make the pizza, preheat oven to 425F/220C.
Knock back the pizza dough (prod with your fingers after turning it out of the bowl) and divide into 4. Keep the pieces you are not working with to one side, covered, while you work on the one pizza.
Roll out the pizza dough into a circle or rectangle, as you prefer, and as suits your baking sheet/tray. Roll it about as thin as you can, transfer to a piece of parchment paper on top of your baking sheet/tray. (Note you can pre-heat the baking sheet and then slide the parchment on to it just before you cook. This may help it cook more evenly but from things I have read but I haven't done a side by side comparison).
Spread the squash puree over the pizza dough so it is fairly even and leaves a small rim around the edge without the paste. Thinly slice the pear then lay slices evenly over the squash mixture. Add drops of the bacon jam in between then sprinkle over the cheese.
Bake for approx 15-20 minutes until the dough is browning and the cheese is just starting to brown as well.