Stir the apple pieces into the mixture. Spoon into the pudding basin and smooth the surface. Cover the basin with the circle of baking parchment, with the pleat in the centre of the pudding.
Cut the lemon in half and squeeze into 2 bowls. Peel, core and chop the apple and toss in the lemon in one bowl. Peel and quarter the pears, remove core and chop and toss into the other bowl of lemon.