Preheat the oven to 180°C/160°C fan/gas mark 4. Grease and line a 2lb loaf tin.
Peel and core three of the pears and chop into rough dice. Put them in a saucepan with a splash of water and 1 tsp cinnamon. Cover and cook over a gentle heat until the pears are soft and the water has evaporated. Remove from the heat and leave to cool. When cool, blitz in a food processor until you have a smooth purée.
Whisk together 75g vegetable oil, 4 tbsp maple syrup, the eggs and Greek yogurt in a bowl. Add the pear purée and the grated parsnip. Stir well to combine.
Sift in the flour, baking powder, bicarbonate of soda and remaining cinnamon. Carefully fold the flour into the remaining ingredients until well combined. Pour the cake batter into the prepared tin. Core the remaining pear and slice into thin slices. Place these in a line along the centre of the cake.
Brush the cake with the remaining oil and bake in the oven for 55-60 minutes, or until a cake skewer comes out clean. Remove from the oven and, while the cake is still hot, brush the top with the remaining maple syrup. Leave to cool in the tin for 15 minutes, then remove from the tin and leave to cool completely.