Preheat the oven to 180℃. Line an 8'x 8" square baking tin with parchment (make sure you leave parchment hanging over the sides to help lift the bars out) and grease with butter.
Melt the butter in a wide pan and add the guavas, salt, lemon juice and chilli powder. The guavas will give out water. Cook for 5 minutes on medium heat till they're done but still hold their shape. Mix the cornflour in 1 tsp water and pour it into the cooked guavas. Let it thicken the mixture and take it off the heat.
To make the crust mixture, whisk the almond flour, salt, cornflour (cornstarch) and sugar together in a bowl. Using your fingertips, rub the butter into the almond flour till they resemble breadcrumbs.
Press this mixture evenly into the prepared tin and bake for 15 minutes till lightly golden and crisp.
While the crust is baking, make the cheesecake batter. Whisk the cream cheese and yoghurt in a bowl till combined. Mix in the sugar and cornflour followed by the egg and vanilla till you have a smooth batter.
Pour the cheesecake batter on to the just-baked, warm crust, and even out the surface. Dollop the guava filling to cover the surface of the cheesecake. Bake for 40 minutes till the filling is mostly set. It might still have a little wobble in the centre. Switch off the oven, open the door and let the cheesecake cool inside for 20 minutes.
Remove the tin from the oven and set on a wire rack to cool completely. Once fully cooled, cover and chill the cheesecake for 3-4 hours in the fridge. Then, lift it out using the overhanging parchment and cut into 2"x 2"squares. Store in an airtight box for up to a week in the fridge.