Half fill a medium-sized mixing bowl with cold water. Cut the lemon in half and squeeze into the water. Preheat the oven to 200C/gas mark 6.
Peel the pears and halve them from stem to base, then remove the cores , adding each fruit to the acidulated water as you go.
Pour the maple syrup into a jug or mixing bowl, cut a couple of strips of zest from one of the oranges and drop into the maple syrup, then squeeze the remaining oranges. You need 150ml of juice.
Stir the juice into the maple syrup. Drop in the long pepper and vanilla pod. Remove the halves of pears from the acidulated water and place them in a baking dish where they fit snugly, cut-side up.. Pour over the maple syrup, orange juice and spices.
Bake, uncovered, for 45-50 minutes until the pears are thoroughly tender to the point of a skewer. Check their progress every 15 minutes or so, as the exact timing will depend on their ripeness.