Whisk the sugar, eggs, olive oil, lemon zest and a pinch of salt in a large bowl.
Gradually incorporate the flour and baking powder until the dough begins to form.
Transfer the dough to a work surface and continue to add the flour, whilst working the dough with your hands until you have a smooth even dough (you'll probably have some leftover flour, it's ok). Flatten into a disk, wrap with cling film and store in the fridge for 30 minutes.
Preheat oven to 170°C /340°F (or 150°C/300°F with fan option on), and arrange the oven tray onto the middle shelf.
Roll the dough on a lightly floured surface, until is about ¼-inch (½ cm) thick. Transfer to an 8-inch (20 cm) tart pan. Trim the pan of any extra dough and prick the base with the tongs of a fork.
Spread the pastry shell with enough jam to cover the base fully and evenly.
Use the remaining dough to form long strips or ropes about 2 cm large (⅔''), and arrange half of them over the base.
Arrange the remaning strips over the first ones forming a crisscross pattern.
Bake the jam tart in the oven for 35-40 minutes, or until it's golden on top. Remove from the oven and let it cool completely before cutting into slices.